Soak them in MEK in a jar overnight. The two-sided foam tape falls off easily the next day.
I attached mine using Automotive Goop (available at the auto parts store). It never dries hard, and is very strong.
Another bit of advice is when you mount them, put a scap nylon ziptie through the hole you intend to use. Once dry, it can be a pain to get a ziptie through. If one is already in place, you can work it back and forth to remove any adhesive that had gotton too far up into the nylon cable mount which could interfere with the tie going through the holes.