A better shop will fit if needed with 2 drill bits sizes being used for your thumb, my thumb hole is smaller at the bottom than the top with ovaling added.
Then we make a few of the molds and keep them around for future use, perfect thumb everytime.
Have thought of trying the Vise IT system but would cost a mint i dont have to fix my fav's, it would be good for 4-6 ball arsenal but in my case that would never work.