Chris,
besides repeatedly announcing as you do to "put your hands together for such-n-such", i have also tried to condition my regular singers to always clap and tell them it helps me do my job.
I've also put a sign on the singer tv screen tht says " please don't scream, swing the mics, dance around, and please applaud for other singers,"etc...
I have found the BEST way for to me to solicit an applause from the crowd is to have a white cardboard sign written in black ink the says "HUGE APPLAUSE!" on one side, and "SOMEBODY SCREAM!" on the other. Has worked for many years now.
Just flash it behind the singer during an instrumental break or right before the end of a song but try not to get caught- they always think they're doing great and it energizes them more to perform.
...i borrowed (stole) the idea from a kj in myrtle beach about 6 years ago. works great!
Try It and you'll be pleasantly surprised! Aloha! J.R.