I have not been on this forum for a long time, sickness and all, and I do not know your expertise with Bonsai, but the plant you are talking about is a fast growing vine. Where I live they grow every where and by most are consider a weed to the point of being noxious.

There was a gentleman in the previous town I lived in that had trained five of these plants to a post and with trimming and training had five beautiful trees, which where in bloom all summer. Having said that, I figure that this plant in a bonsai form would probably have the same needs of a weeping willow bonsai. Not in possible to do, but requiring a lot of work, to keep in a bonsai form and you might have trouble wintering it, depending on where you live. Also any situation is that they propagated by runners and are always sending up shoots, something else you have to deal with.

Hope this helps and I would be interested in your experience with this plant. As you said a large bonsai would be the way to go with this plant. I have done same thing when I used a honeysuckle vine. I used a number of rooted vines and they eventually grew into a soild trunk which was an interesting look.

Have a great day.

Tom L.L.