Making Suction Cups Stick In Shower What Can I Use To Make A Suction Cup Stick To A Non-flat Surface That Will Not Permanently Damage The Wall?

What can I use to make a suction cup stick to a non-flat surface that will not permanently damage the wall? - making suction cups stick in shower

I know that with a suction cup on a flat wall is not in contradiction to the goal, but that's what I have to work. We bought a hand-held shower. The owner requires it to work for a flat wall. We do not have smooth walls in the shower. I can not get an adhesive that will not hold a commercial grade adhesive?