A friend of mine who is an officer taught me about the nystagmus. I trained myself to follow a finger or pen, but when I get to where it feels like I'm starting to "force" my eyeballs to the corners of my eyes I would stop forcing my eyes to turn. thereby avoiding the nystagmus.

I got pulled over after two drinks one night, (I rarely drink more than two and drive home) for rolling through a stop sign. totally stupid but my fault. the officer smelled the beer, then gave me the full check. when I followed the pen, I stopped my eyes when they felt labored from forcing to the side, and he told me to keep following. I told him I cant force my eyes anymore they wont go. he asked once or twice more and I still denied. finally he let me go. it was a little nerve wrecking.