Hello,
I've been thinking the same thing. My Clemantis Montana is going over to seed and my thinking is that it must be possible. As surely plants find a way to survive without us? So some of those seeds, given the right conditions must grow into new plants over time.
Having said that, I do think the best way is to take cuttings from existing Clematis plants. I have some brilliant advice on here and am doing my trial of cuttings...... so far none of them have keeled over. I think for some plants cuttings is the way to go.
I'll have a look and try and post a link to the advice I was given.