Not really much. You could be the owner of the game and give the real GM GM rights, then the game has all the mentor features. After logging in you'd then "Join as Player" from the setting tab. Some stuff is limited to the owner though, not sure if the other GM can see the API etc, but it would be there and you could definitely access it. Of course there's no way to transfer ownership, so you'd have to recreate the entire game. However, if you're not willing to do that (or your GM), then aside from the fact you get access from mobile devices and maybe some other small goodies there's not really a benefit for players from mentorship. If it's the same GM, you could also think about gifting a mentor sub to the GM.