Ditto that last post. If your voice can't make it to the mic there's nothing I can do for you.
If I were to reach in my own box I'd probably grab two or three
Shure SM-81 condensers to hang up. They're a full sized mic though so you have to keep them up out of sight. Or some SM-91 mics along the front of the
stage. Trouble with any of those is that if Uncle Ed coughing in the fifth row is louder than Little Sally Stagefright you get it in the mix. Same goes for the musicians in the pit.
Almost every manufacturer also makes some type of "choir" mic which is generally an
omnidirectional condenser and almost completely useless for anything other than recording a chorus concert. Using them live is sheer hell unless your aud is accoustically perect. Usually the talent on
stage in a high school show makes things even worse with the
level of consistency you usually get.
In lieu of all of that I've had some pretty good luck on shows where the director cast a few "pit singers" to flesh out the cast. Usually it would be one of each voice (Soprano, alto, tenor and
bass), sometimes more if there were a ton of parts. We'd usually seat them with the woodwinds (as far from the brass and percussion as is
practical) and I'd give them each a
dynamic vocal mic on a stand. They could get very close and give a very good signal. I'd do a little trickery with the
effects processor to make them sound like more people than there were, and in combination with the voices on
stage it sounded like a million bucks.
Of course you'll never get it to fly if it isn't the directors idea and they come to you. Always worth putting a
bug in their ear and seeing if they'll keep it in mind for futurre shows, especially after they see what a crap job area micing does on
stage.