Easily removable material that sticks to skin
I have an engineering solution for you that bypasses the need to find a chemistry solution.


  I'm thinking more along the lines of a sticky polymer sheet that readily sticks to the skin 


You want an adhesive bandage. Adhesive bandages are thin, stick to skin, and are easy to remove. In my experience, the less expensive generic brands are both thinner and stickier, so go with a generic brand. If you are worried about the thickness, do not use the central part with the embedded gauze pad. Only use the wings. Use a strong glue to fix your motor to the back of the adhesive wing.