Can you not just do some photoshop magic?
ie: have both images (short exposure and long exposures) as different layers, and select the burnt out core of the long-exposure and cut it out, so when you flatten the layers you'll get the less-exposed core from the shorter images?
Both images will have to match exactly in every other way I spose, but with your tracking mount that shouldn't be too much of a problem I'm guessing.
