if you choose to go for a root-over-rock style then you should let the roots develop for a few more years(2 at least) and then get a nice looking rock(with many holes,cracks,crevases) and wrap it with roots.Don't use any rock, remember that it's a root-over-rock style, and the rock is important.here's what you have to do to get a nice root base:
1
rill some holes in the current roots/lower trunk add rooting hormone in them and bury the tree deeper.
2:take some ficus seedlings(same species) and plant them near the trunk, carve a little of the trunk out and use duck tape to join the seedlings and the trunk together.After a few years, they should fuse, and you can remove the seedlings foliage leaving only the roots.
Jerry's site has more info on grafting roots i think....
About backbudding:
Let it grow freely for 2 months, fertilize aggresively. Then hardprune all the branches.