I have actually made it on top of a pretty flat and useless grip I bought from Olympus, so in this case there's no doubt whatever that I can get it off again without remains. :-)
Here is a grip/ridge I made for tablets before I found the SG sheet.
Also, to reiterate: Such a grip, if you have followed instructions about putting on Sugru, will not fall off in your hand. It's a cousin to super-glue, crazy strong. (Sugru tips.)
(btw, I have just modified the top to have a stippled, almost fuzzy, surface. It meshes better, and it hides the unevenesses which I had to give up removing totally.)
I must say, that in terms of pure grip functionality (if you don't count the big, integrated grips on the big SLRs) this is far better than any commercial grip I have tried.)
The camera before:
Below, alternative surface, made with light stippling with toothbrush. It makes it mesh better and hides unevennesses (which can be tricky to get rid of).
By the way, on both cameras, I have also put the Sheet on the little, flat thumbgrip on the backside. Makes it easier to find with your thumb, and improves the hold yet a little bit.
After it cured fully (24 hours), I tried to rip the grip off. Okay, not with my full strength, I am a quite big fella after all, but I couldn't budge it. There was not a hint that this was not there to stay.