Maybe one of those half wine barrel LARGE containers? And maybe a clematis that can grow up into a tree. Not all clematis will get very large. You'd have to do some research, but maybe a "montana" clematis? Or a Sweet Autumn clematis?
How tall is the maple tree? A montana clematis can grow to 30 or 40 feet, some of them anyways.

Montana would not grow and/or bloom in zone 5.

I absolutely agree with Judith about Maples - they are notorious for killing other plants. Norway and Sugar maples especially. I do have some Epimediums and Geraniums planted under my Amur Maple, but even these tough guys do not thrive. Clematis is definitely is not a good candidate for this.

I would try a wild grape vine, I have one of these and nothing fazes it!
-B

I have trained clematis to grow up all my mature tree in my yard - several maple, an ash, an elm, and a cherry tree as well- I cut and wrapped chicken wire and stapled it to the side of the tree. the wire rusts to the color of the bark after one season. I dug out a good hole much larger than needed next to the trunk where I was to plant my vine. I filled with high quality manure/compost and top soil and packed tight. I water them with the hose when I am doing the normal rounds in the yard and I have "bricked" a small boarder around their base to help hold some water at their roots. I also leave little "presents" for them of dried out/old dog droppings maybe once or twice a year near them to leach some natural nitrogen for them - they seem to love it and always give me a nice bright green burst of growth when they get their gifts and a good rain :-) I do admit on the oldest maples it was hard at first because the trunk runs outward and soil was shallow - but the brick border helped build enough base for them to get established.

good luck - nothing prettier than a flowering trunk on a beautiful tree

cytis01,
Could you post a picture of Clematis planted next to the maple please? And blooming? I just have to see it :)

I sure will - they arent blooming yet in my corner of Minnesota - its been a pretty cool May thus far too- I will try to remember once they are going-

I have Guernsey Cream, Niobe, Polish Spirit and now a new Pearl d'Azur all 5' or closer to on of my red maples. Guernsey doesnt get HUGE, but it flowers like mad on the fence above hosta and bleeding hearts.
If you have trouble digging to plant at the base of the tree, dig what you can without damaging the tree roots,(you may have to make a few test holes to find a good spot) and loosen the soil around it, so your clem roots can anchor in easily. Lay the roots of the clematis carefully into the hole, tucking them in and around the roots of the tree. Use purchased soil to mound the area up if you cant get down far enough. But if you put new soil around it, REALLY tamp it down hard to compact it, and check periodically for upheavel until its established. Its ify if you cant get down deep enough.
Find a Clematis that takes partial shade.
Good luck.

You are giving me some hope guys. I have a Red Maple on my front yard. My mail box is about 5' from its trunk. I gave up the idea of planting a Clemmie next to the mail box. I might try now... I also have an Amur Maple on my backyard. My Epimediums and dry-shade-tolerant Geraniums are OK there, but not thriving. I just planted some Purple Dragon Lamium under it. Same thing - it does not die, but id does not spread either. Maybe, I should try that Maple first. Would be nice to have a Clematis climbing its trunk. Will buy a couple of unexpensive group III from Bluestone 50% sale this year to experiment :)

Would really appreciate pictures from both of you (under-maples-Clematis-growers).
I wonder if the Clematis roots grow deeper/below maples' roots?

I too would LOVE to see pictures of clematis growing up Maple trees please. I am in Nova Scotia, Canada, and have a Jackmanii that I would dearly love to put in. As for Maples not being friendly to other plants, its not the case here :) I have Azalea, Rhodies, Astilbes, Hosta, Primula, Weigela, Irises and the list goes on :)

But please Cytis01, if you would...I'd like to see pics!

To cover the scar on the maple, you might try climbing hydrangea. It is relatively fast growing and adheres to the trunk with aereal roots somewhat like ivy.

Depending on how much sun it gets, I think, it takes several years to start flowering. I have some covering the south east side of an arbor/arch that does flower, but a division of it that is climbing an enormous ugly beech does not, however it has nice shiny leaves going from the base to about 20-30 feet up (about as high as the electric wires across the street, I'm no good at estimating height.)

I believe there is now a variegated foliage available now, but it is probably not as hardy or vigorous.

If you decide to grow a clematis in a container, below is a link to a thread about that. You'd want a plant hardy to zone 3 if you don't want to fuss with winterizing the container. I had a whiskey barrel planter under a red maple and the maple's roots grew into the container, so I'd recommend raising the planter on bricks (my current solution) or putting a saucer under it.

Here's a thread that looks at various clematis supports, including one photo of a copper pipe spiraling up a tree trunk:
http://forums.gardenweb.com/forums/load/clematis/msg0511513616418.html

If you decide to go with a climbing hydrangea (no support needed other than the tree trunk itself) here is a link that covers variegated hydrangeas:
http://forums.gardenweb.com/forums/load/neweng/msg061050018927.html

Here is a link that might be useful: clematis in a container