I do not think this maybe a good idea. The GMAC would have already considered the pros and cons of the whiteboard. They've done their best in terms of conducting the exams in a secure manner. The whiteboard is needed as it can reduce the chances of cheating. In addition to that, from my own experience, I can say that I was comfortable using it after practicing on it for a while.
As far as being a consumer is concerned, I totally empathize with you. This feels like another obstacle needed to get through, but keep in mind that the GMAC has done their best to not let leave the test takers' efforts go in vain. With this I hope that you achieve the score you desire.