I would think that your best bet would be to give it time so as to not stress the plant.
However, layering is basically what you are talking about which can easily be done on most all of the larger ficus sp. Basically all you do for that is notch the bark all the way around the stem, apply rooting hormong and moist sphagnum and wrap it with something to keep the moisture in and roots will form, and I would guess from there you could get the roots to grow down to the soil. However, at this point, that part of the plant may grow completely seperately from the rest of it depending if you cut through the xylem and phloem layers.
If you have a greenhouse, or somewhere you can put it with a high humidity level, that will usually promote more aerial roots to grow naturally.