Cooking cakes with Pop Rocks / Space Dust
Never tried anything like this, but you asked for ideas...

Can you even frost the cake with them w/o them reacting? If they only react w/ water, you may be able to get them in a fat-based frosting. Especially if you use this for the middle frosting of a two-layer cake, this may work.

If you really want them in the cake itself, and they don't react with the baked cake (it has water still, I bet they do) you could make a double-layer cake, and insert them into the hidden surfaces (e.g., the bottom of the top layer and the top of the bottom layer). Just make some slits and put them in.