The cheap solution, and perhaps the best, is to get a laptop hood/shade.
Even with non-glossy displays, these things can be indispensable in certain cases because no matter what, uneven and inconsistent lighting can be a SERIOUS headache. As well, you'll save on battery and backlight-life because you won't be battling it out with external light.
If you're on stage you probably can plug your MacBook Pro to a power source, right?
In that case just max out the brightness and there will no problem, i think this problem is overrated or at least i underrate it, at home i have the brightness on auto, which basically has it at 50% without a problem