I've been thinking about this Nicole and while I agree with much of the sound mudcat advice given on this thread ,the simpler solution would surely be to take along a recording of the piece in question on the night and play it while miming .
Some of your fellow choir members may find that this is "cheating" , a thing I am sometimes accused of when I bring a tape recorder along to trad sessions in my local pub . Against that it can be said that the overall quality of the recording is often of a higher standard than that of the so-called live musicians.