Had a similar issue. Started with one, then ended up with two, then four and it wouldn't stop. Ended up with a peak of 14 and currently holding steady at 5 after losing a few in a tank migration and giving some away.
Unless they are on the tanks wall it is going to be a challenge because they can get their foot attached in some pretty deep crevices which makes it difficult and unsafe. I ended up just giving the rock and all away much to my dismay. Considering doing it with the remaining or moving them to a refugium.
Things I have tried:
1. Steady stream of random yet gentle water flow. Not blasting them but enough to see if they will move. May take time but possible to get them somewhere so that you can peel off.
2. Ice cube under foot. Have to be quick and in a place to reach without harming you or the nem.