The hero wouldn't be able to leave or be unloaded if it's devoured. (I think. Haven't paired devour and unload together before)
Alternatively, you could GUI or Script it yourself, which may be the least messy way.
To do that easily, you would need AutoIndex and AutoEvents, and perhaps a little knowledge of JASS or GUI + Custom Scripts.
You could do it without those by creating your own load/unload abilities. When you use the load ability on a unit, you store that unit in a variable and hide it. When you unload it, or when the unit dies, you move the unit to the unloading unit and unhide it.
While it's hidden, you heal the unit.
For more details on how to create something like that, ask in the Trigger zone.
I used something similar in my 11th Vampire map with the Osirian Vampire.