I just bought a clamp-on cup holder and attached it to the back end of the mic boom. It faces the audience and hold a cup very securly, in plain view of the people.
I've said before that the more electronic I seem to be, the less tips I make. This is still true. There's nothing like a big brown, wooden box to attract tips. The plastic gear just doesn't seem to evoke the same emotion in the crowds.
Nevertheless ...... now they has a stash that they can contribute to !