One approach is, instead of making cake out of Space Marines or Boltguns, is to make the game board (known as terrain) into a cake, and then stick models to it.
This one is courtesy of Takkaryx on the SA forums. It has no models on it, but is absolutely ‘terrain’.
US-based professional cake makers Arteatsbakery makes the models part of their edible battlefield.
And finally Vallum House Cakes combines scenery with hand made edible models to produce this.