This requires alot of unit edit work in the object editor.
Atm, its very easy to just add halftrack loading options to a tank. Im sure you could do it to any model, but to have them sitting on top; that's a whole new monster and the object editor is very a very mysterious and ancient artifact.
Only a select few chosen ones still know how to operate the bones and animations. It just looks like voo-doo witch craft to me.