I used a coffee grinder on the pellets and old fashioned oatmeal. Add a little water to make it mix and put on a ceramic plate. Scamps ate like this for 3 years before we had to euthanize him.
Pinto had a bladder stone last year. A little smaller than the largest one you posted. Sent it out, came back 100% calcium carbonate. He is on Oxbow adult cavy food. So far so good! He did have to wear an ecollar the first few days to keep him away from his incision but after that he was...
I could never do it. Having said that I totally understand why people would want that. It doesnt matter what people say. Its your pet, and how you chose to remember them or memoralize them is your choice.