The kind of plant can vary with where you're going to keep the pot. If outside and not in full sun, ivy is good. For me, at least, if I have ivy inside, it always gets spider mites. You can do a google search for topiary plants to get other ideas.

Vines with smaller leaves give better definition. Creeping fig may be used. Use hair pins (like bobby-pins) to secure the vine against the stuffed frame. Make sure the moss isn't loose, otherwise it'll dry out really fast.