Im not sure it can be done at all
I think it may be too big a break with convention, so a workaround may be the only way. I'd go with the Hover thing, and try to figure out a way to stop AA stuff treating them as Air Units, maybe by making sure they are the only unit with a certain Armor= (medium). Long winded, but possible I think?
The only way round the 'coming out of hte roof' thing I can suggest is giving it Naval=yes so the unit has to come out of the Naval Yard.