A polarizer could very easily be the answer to your question -as pointed out by keerok. A polarizer will only work if the light source is at or near a 90 degree angle to the plane of the sensor. In other words, if the light is directly overhead (90 degrees) then the polarizer will be at its most effective. As the light source moves forward, towards the glass white board, the polarizer becomes less effective. This can be seen when photographing landscapes. With the Sun directly overhead, the polarizer really darkens the blue sky, but when the Sun is in the frame, say when taking a sunset shot with the Sun near the horizon pointed directly at the camera, then the polarizer has zero effect.
So a polarizer should help, maybe even a lot. However, to do this without a polarizer, one would have to either turn the lights off (not sure if you will be able to see the board with the lights off) or ensure that all of the light sources are at a 45 degree angle to the plane of the white board. This is basic lighting 101. Angle of incidence (the light source) equals the angle of reflectance. Therefore, the glare that you see will only be visible if you stand at a 45 degree angle to the board. At 90 degrees, you see nothing but a nice clean, reflection-free board. Trick is getting the lights at this angle is not always feasible or possible.