I've never done it, but I've seen it and it's pretty. One of the rose nurseries in Garden Watchdog's Top 30 list has suggestions for companions. Don't remember which one, but there are only a few rose specialty nurseries in their top list.

I've seen several people in the clematis forum post pictures of their rose/clematis combinations, so you might check that out too.

I've never done it either but I just planted a different color clematis to accompany the one I already have and I planted it about 7 inches from the existing one. Of course the one I had was already there and I didn't want to disturb the roots. I'm not sure it would matter since the clematis has such a thin stalk. Just my opinion though. I like the idea of the contrasting colors and foliage.

I had 'The President' growing in a 'Cl. America' in my last garden. I wish I'd had the foresight to plant clematis in ALL my climbing roses! I'm starting a new garden here in Georgia, and I plan on planting clematis wherever I can.

Make sure you check the pruning cycle of the clematis. Some bloom on old wood only, so if you cut back the vine each year, you'll never have blooms.

Some bloom on new wood and some on new and old wood. Both those will do well with your roses.

I have a list I've put together if anyone's interested.

Almost every single rose I grow has a clematis to go with it. The buff/apricts have texensis in pinks and "red" which is more cherise in my garden, the yellows have purple. Earnest Markham has not bloomed with the Knockout yet, so it could be good...or not...
I have two the same color cl. Cramoisi Superior with a similarly colored clematis which is gorgeous just for contrast of petal shape...Mozart has Rouge Cardinal, Monsieur Tillier will have dark purple velvety clematis (I've forgotten its' name...) I have 14 pairs of clematis/roses going now... I'm hoping for a very good show this year.

GGG

I've been doing it, too. I don't plant them in the same hole, but plant the clematis out along the branches of the rose. I, too, like purple clematis with yellow roses, and I'm trying to get two red Niobe clematis to grow with my white Lady Banks but they're a little slow coming along. Just recently I planted a dark montana clematis, I think it is Freda, beside my Veilchenblau rose, and the clematis is blooming beautifully now and the rose is in bud, so I think this will be a nice combination. I've also got a lighter pink montana clematis on an arbor with a yellow lady banks rose and that looks really good right now - both are in full bloom. I am a new fan of montana clematis with their smaller flowers and think they will go really well with roses because they won't outshow them. A lot of the larger-flowered clematis are just really too showy when the rose is in bloom, although they're nice with once-blooming roses because they fill the shrub in with color after the rose has bloomed.

I planted 2 clematis jackamani on either side of an arbor w/2 lady banks roses. I get more compliments on them than any other area of my yard.

I also have planted a couple of my roses with clematis.. I have jackamani with a climbing Don Juan and a jackamani with John F. Kennedy.. They look awesome together and noticed both have extensive buds this year.. I planted my roses first, let them have a year to root and then planted my clematis near them..

To do well try to plant your Clematis where the roots will be shaded. They like cool feet here in Georgia.