Not a whole lot you can say other than "it's not a true reflection of my ability" and no matter how hard you try to justify it with tomes of evidence, the reality is the adcom will either overlook the score, or he/she won't. Nothing really is 'effective' to get around it.
GMAT is like height to basketball. Being tall won't automatically make you a great player, but being short can be a significant barrier to getting on the team - based on your overall skills as a basketball player, the coach will either overlook your height, or he/she won't.
The only way to mitigate a low GMAT score is to re-take it and get a better score. If this is however the best score you can get (some people just simply aren't good standardized test takers), then there's not a whole lot you can say -- and all you can do is to make sure your essays and rec letters are exceptional.
I know it sucks to hear that, but that's the reality.
Alex Chu
alex@mbaapply.com
www.mbaapply.com
http://mbaapply.blogpsot.com