Question
Is there a method of promoting the growth of air roots on Ficus trees?

Answer
Depending on the age of the  plant, you can bury it in a large pot, so that up to two thirds of the trunk will be covered. New roots should appear in a few months. After that, select the ones you need and wrap them in sphagnum moss.Give them water and fertilizer until they can reach the soil of the original pot.

Please look into "Air Layering"

      Good Luck !