Hey Catherine, you can use double sided carpet tape to stick them to a board with a runner on the bottom that goes in your ball vise or just set in on a non slip cushion like what you put in the bottom of tool drawers.
Catharine, Mike Dubber has an excellent video on the net somewhere about cutting large platter with monograms, just can't remember where that video is located . Here or over at the Lindsay site or it might be on Christians site. Sorry I don't have the time to look for it right now. You might check Mikes site and drop him a personal contact. He did that kind of work for 40 years. Fred
Sandbags work good. Buy them or have them custom-made. Shoe repairman can make them for you out of leather. Rotate your objects on the sandbag. I've also seen Mike's video. I believe he used sandbags and it's very good.