A mic without a lot of top end, like a SM-57 would work. It's not as inclined to pick up the cymbals. I used a 56 because it had a pivot head. Not enough to wreck the tone on the vocal, but enough to get rid of the cymbals.
Same things apply to the front vocal mics.
They could be picking up the cymbals too. If budget allows that would work the best I think. It tells you in the manual that the mic should be touching the mouth at all times, so it doesn't pick up other sounds. The more inexpensive mics may not work as well. Probably have to test them out on a gig to see how well they work.