Unit which can attack when loaded with hero?

I'm working out the mechanics of a character for a map I'm planning. Here's the basics of what I need:

1) A unit which cannot move or attack, but has a cargo hold (or something similar)
2) A hero which can be loaded into the unit, but only once the appropriate skill has been learned.

When a hero is loaded, the unit now needs to be able to move and attack. Also, the hero should be able to unload, thereby reverting the unit back to the original state.

I'm thinking this is somewhat similar to what the Pilot Tank features would have been (which seem to be completely removed from TFT). I have looked at doing it with the hippograph commands, but they appear to want a specific unit type, and I'm not sure they would work with heroes anyway...

Additionally, would it be possible to have the hero gain Exp while loaded into the unit?

Thanks,
Trick