My son is working for a company that does detailing/restoration on high end automobiles. He’s doing repairs that involve removing curb rash from wheels and restoring the color. In most cases the wheels are still on the car so the repair involves squatting while smoothing off the rash and repainting the wheel. What are good stretches/mobility moves to help him avoid soreness from this activity. Note he works weights on a regular basis, no known knee issues.

Would something like getting long term comfortable in a 3rd World/prisoner squat be helpful? Appreciate any thoughts.