If it’s a simple enough mask, and/or there’s not much movement to it, you could put a null object at one of the mask points and then use one of several scripts out there to link the mask point to the null object. Try here or here. Then you could just link the flare center to that null object.
As far as I know, there’s no way to extract the mask point data from the mask, though – I’ve put in a feature request to Adobe for this more times than I can count. I’m not even close to being competent enough writing code to be able to say this with an authority, but it seems to me it would be pretty straightforward for every mask point to have a 2-3 value array to define its position, so that you could get in there and monkey with it or reference it as you’re trying to do.
Good luck,
Steve