Fewer moving parts the better in my opinion.
I like the idea of magnetic contacts but from what I gather is that you need to be careful as they can snap together and pinch if your not careful also.
In either case, Cohesive bandage would be a great cushion or buffer to protect the ball sack from getting pinched and also allow some air circulation. Although that might take away for the sensation of contact with the steel surface.
Cohesive Bandage does not stick to the skin but holds well when in contact with itself. It is easily separated for removal. Perfect application for the job.