Moving unit undergound (negative flying height?)

Is there any way to move a unit underground using triggers? My initial googling seem to indicate that it's only possible to change a units flying height to negative in the unit editor and impossible ingame using triggers. Just asking to be sure.

Asking because I was trying to find a way of making a spell that "melts" an enemy. Was going to do it by turning the targeted unit green and lowering into the ground while creating a green patch (custom art) on the ground that i scale up.

It's impossible other than in editor