Had the same problem and got annoyed to the point that I bought a setup from Proclip.com. Not the cheapest solution but 5 years later still works perfectly. FWIW, I bought a wireless charging cradle for my phone, it came with a ball and socket connector so it worked with the Proclip mount.

If you won't need to remove it regularly, use 100% silicone. It acts like a liquid to make it stick well in the short term, and when it dries it is semi-permanently attached. Just rub a dab on and stick the cup like normal.

I like silicone because it is an excellent adhesive, but unlike glues it stays rubbery and can be removed completely later. (at least for hard, smooth, non-porous surfaces like glass or steel)

As in all things adhesive, prep work is important, so wipe area and the cup with alcohol and allow to dry completely before sticking it.