I've thought about backlighting too but primed canvas is fairly opaque and although it would shine through a little bit, it wouldn't be suitable as the sole source of light, or as an accent.
This is what one of the performances is generally like:
It's mainly black on white, so the LEDs would serve two purposes. One would be that hopefully while in 'white' mode, they could replace the clunky/hot workslights we often use to perform with.
They work well as most places we perform in are dark, so having a bright painting is a must. The worklights, as mentioned, are very hot and uncomfortable to look at, and also cast shadows (even with two of them).
The other thing would be to shift the mood/color of the light to red or blue (or whatever) based on manual control and/or eventually some accelerometer/gyro type setup on the artist's wrists.
Just to add another dimension/element to the performance.
We'd have to be very careful for it not to become a disco show, but I think colored light could be very effective.