I have a few little ficus that I have been growing from cuttings last year. The trunks are still very small, the biggest being as thick as a couple pencils. They have been growing well since I out them in actual pots, but I don’t think they’re ready for bigger pots yet. So in order to create a thicker base, or at least the illusion of a thicker base, I am trying to induce some aerial roots low on the trunk. I soaked some sphagnum moss and packed it against the base of the trunks, then covered with aluminum foil. Hopefully the moss will help some roots pop off the trunk.
Hopefully by the time I have to bring the ficus in for the winter they will have sprouted a few roots and I can remove the moss.
Indiana Bonsai 
I want you to look at some asian and chinese figs…They try to create most of the trunk from roots, since roots of figs grow very fast. They even fill in between the roots and expose them to create a trunk while thickening. Air roots are also a plus. I have done similar thing but I tied it up on the trunk with plastic around…Haven’t checked out how it is doing…
I also get just a plastic packet like a dome, going down over the edge of the pot….but tied bellow the leafs…to create extra humidity.
Any update pics about this? Did this work?
Unfortunately it didn’t work. I suspect the tree wasn’t growing healthily enough.