I've read that avocado can be grafted this way, so I tried it a while back.
It was much easier to graft an avocado than a green sapote (or canistel)
The root system was easier to work with. If the tree lives I'll post some pics. I think the chances are very good for success, but I don't know what it will do to the tree.
Maybe it will end up with some mickey mouse looking callus! (like Cookiemonsters tree!) Its fine with me as long as the tree fruits quickly, and stays small and healthy.