One alternative (if House Management will allow it) is to set the bubble machine in the audience. If the bubbles never hit the stage, you don't need to worry about cleanup, and the effect can be just as pronounced if the bubbles emerge over the front row (or even from behind the audience--just remember to start the machine a good 20-30 seconds earlier than you otherwise would, and perhaps use paper fans to help get the first few batches over the audience quickly).