I've recently had to learn "The Floating Thumb Technique" after moving from 4 to 5 string. TBH I should have leant to play this before changing to 5ers - long term I would expect fewer issues with hand/ tendon injuries.
I'd suggest learning this rather than putting screw holes in your gear. @TJ1 If you choose to go down the thumb rest route let me know. I have one I took off another bass.