Great idea! I have found gaining by adding just a few hundred (thousand) calories a day consistently works well, not huge gain, but a few pounds here and there, plus prevents stretch marks.
And if you could be lucky enough to find a DD that carries the full selection of varieties you could score 6 of their Chocolate Coconut Cake at 550 calories each. There are also some at 490 calories each and one around 520 I think. But those varieties are hard to find at most DD's.