I've used clear acrylic nail polish (sold as strengthener). Put ring in place, roll back one side, apply, roll back the other side, apply. Two concerns would be if the nail polish eats away any paint on the lens as it squishes out from the edges, and if the lens is plastic and melts. Let the lens air out for a couple of days no matter.
Another material I like for such things is called 'transfer tape.' 3M makes it. Basically a thin film of a rubber cement-type of adhesive in tape form. The problem with it is that it is very sticky and can drive you nuts while first learning to use it.
The thing i like about both of these glues/tapes is that they allow for removal. The acrylic will basically 'snap' after it dries but still holds a collar well. The transfer tape stays gummy and flexible so you can pull things away (watch for stretching; alcohol will help it release).