I'm sorry if this is a really stupid questions. I happen to LOVE the cakes from Costco. I would like to purchase one of these cakes for my son's 1st birthday. I would ask them to just frost the cake in their buttercream frosting so that I can cover it with fondant. Would this work? I just would love to decorate the cake myself. Thanks for reading!

You bought the cake so you can do anything you like with it. If the buttercream is a little dry just give it a light spray with water or karo mixed wtih water so the fondant will stick. Just barely damp not wet.

Absolutly - why not?! Sounds like a good time saver too

PS .. There are NO dumb questions!

Thanks so much for your replies...I appreciate the advise!

It works perfectly fine. I bought a carrot cake from Costco w/o the decorations, carved it into a round and decorated it with fondant. You can see it on my pics...its the bottom tier of the pink polka dot shower cake.
Good Luck!