OK, I'm going to answer my own question here in case someone else has this problem. Apparently, you lay the frog on a very hard surface (top of vise jaw if metal) with the back of the lateral adjustment lever facing down. Then proceed to round over the rivet with a ball peen hammer. Take care not to hit the frog and make small precise hits. This will cause the rivet to mushroom therefore tightening the fit. (I think the word for that part is "rivet" though I could be mistaking.) This advice was given over the WoodNet forum.