I have not experience with the dissectums as a bonsai, but I have one potted in a 4-5 gallon planter on the front porch. it is potted in a mix of about 50% potting soil and 50% pumice so the soil is more free draining than dirt (and also much lighter). I am getting some ramification through a combination of cutting/pinching back to the a single pair of leaves/branches and letting it become somewhat root bound. Since these trees have such a low foliage mass I would think that fairly strong fertilization and continuous pinching/pruning back should act like a partial defoliation and encourage ramification.