Unfortinately, there's no way you could make this work with clematis, sorry to bear the bad news!
However, you could try annuals and they might work if the holes are wide and deep enough for the roots. If it's a shady spot, Impatiens may work well, because they have very small root systems. I would think a 3" wide x6" deep hole would work. These require lots of water, though ! Good luck.
Suzy

Thanks Suzie. It's a full sun area. *sigh* Back to the drawing board--I guess I have plenty of time to plan!!

I started 'Radar Love from seed several years ago--it's a C. tangutica. If you wanted to cover the stump with something like netting, Radar Love would grow up over it, though keep in mind that it's a big clematis--up to 12 feet. I cut mine nearly to the ground every spring, since it blooms on new wood. So it the stump were at least three feet tall, you could probably get it to make a huge mound every year on the stump.