We grow our Chinese wisteria as a tree and a few years ago I planted Henryi clematis to grow into it. (see pictures in the link) This is the first year it has made it all the way to the top and put on a reasonable show. The wisteria is branched pretty low to the ground so all I needed to do was lean a bamboo pole into the tree to give the clematis a route into the lower part of the canopy.

Here is a link that might be useful: Henryi in wisteria tree

I have used standard trellises and tuteurs to support Clematis but allow them to climb. As long as the tree is not overwhelmed by a massive vine, it works well. I do not recommend having a Clematis , particularly a vigorous type, climb on a pine or other evergreen. The moisture and spent petals make for disease.
That happened to me on a dwarf mugo pine.
Here's one of the natives on a trellis, then climbing into Prunus viriginiana 'Schubert'.

Thanks for the pics,, can anyone show me how to use a copper pipe or bamboo stick to lead the clematis up the tree? Is there really enough space on a thin stick to lead it up there? My mind is having a hard time imagining this, and my husband is insisting that it can't be done and wants to lean a full trellis against the tree. I was kinda thinking a thin pipe at least a food and a 1/2 away from the tree roots. I'm hoping the Candida Clem will follow obediently!

No photos, but BuyorSell had a single loose spiral of copper pipe that went loosely around the trunk. However, she later said about this:
"My copper spiral doesn't actually work very well. You need something like metal grid fencing wrapped around the trunk or part of it.
or something like this trellis" **see link below**
( from thread here: http://forums.gardenweb.com/forums/load/clematis/msg091028229155.html)

The problem with the copper spiral is that it is a bit fatter than clematis can easily wind around, and there is just the single pipe, which makes the plant more crowded, while the plant would rather spread out a bit more.

Grid fencing held up by rebar and wrapped in a half-circle near the trunk or a trellis along the lines of the one linked below will be more successful. I also use free-standing obelisks set a few feet away from the tree for the clematis to start to climb, and from the top of those they launch into taller shrubs and smaller trees.

Here is a link that might be useful: half-round trellis

You could easily use wire anchored with a rock at soil level.
Send the wire from the rock up to the tree branch and secure it. You could use three separate wires on one rock . It will be close to invisible. Wrap the wire around the rock or brick to secure first.
Your Clematis won't grow next to the trunk of the tree as it must have ample moisture and soil. The tree should be compatible with Clematis - no red maples, Norway maples, or others with a massive root system.