I've found the the best cake in dunkin' Hines devils food cake... I've tried vanilla frosting with strawberry cake (wanted to add chocolate ice cream for a chocolate covered strawberry) and all I can say "STAY AWAY" something with the vanilla frosting and cooking it smelled like eggs :(
If...
You can also prepare the cake mixture before hand and have it in the covered batter bowl. But, why put it in the microwave before hand? I would show the DCB, tell them how wonderful it is, open the batter bowl pour the pre-made mix and scrape with your mix-n-scraper. Scoop out the frosting...
There are a lot of gluten free products/pasta at specialty stores. Fairway, Trader Joes have these items. I would ask a pharmacist and/or specialty drug store about the stone. i would think having it in the oven would kill off everything.
I know this isn't on your list but the Deep Covered Baker is awesome and at 60% it's even better. I make the hot molten lava cake with it. It gets a lot of ohhhs and ahhhs.