use the grinder... It will help and make it a lot easier. It is much easier when the extensions are really short!
Then put the shaver tool over the rivet head and bring it to high speed before you lower it. Don´t lower it on the rivet head before you speed up your Makita or what ever you use, that will make the shaver tool bounce.
Good luck and have fun shaving
600 Olympics is a lot of work!!