I'm thinking you are on to something with that baby powder idea. It should do the trick. Gorilla glue doesn't seem to expand much on its own to begin with, so any flex would be minor. So you should be good on that.
I'm really curious to see how the final product turns out.
I've not really need any repair jobs that turned out with a nice clean finish, but it looks like you are on the right track.
Lucky for my, the only cracks on the Z dash are on the removable part around the cluster.

that tint with be going on both my truck and my DD Z.