I don't reckon your exposure compensation idea will work that well, simply because you don't have enough small steps available to make it smooth. Think about it, if you had 10 second shot on screen and you wanted to compensate 2 stops. You have 300 frames but only 6 x 1/3 steps to use, so every 50 frames it's just gonna jump. If you could adjust by 1/300th of a stop then it would work!
Jon, the problem with your statement was that you missed out the bit about it being the way that works for you. However you read it, it was absolute, there is only one way. No harm done anyway, and again nice shot!
Evan, I would re-emphasize, take power into consideration, long shutter speeds use lots of juice, and you don't want the camera to go dead half way through. Good luck.
Steve

I can't show most of my work due to NDAs, copyright and general laziness on my part. There are a few jobs on my website and below are some random TL shots.