You just need a smaller venue to overwinter the tilapia in. If you had a micropond like Meadowlark's, 100 gpm at 67 degrees would keep the temp up easy; your biggest problem might be non-cooling aeration of all the well water.
I was unsuccessful trying to find ML's micropond thread - hey ML, what's the link?
Also check out Ryan Freeze's Tilapia overwintering in a tank, IIRC on the order of 1500 gallons.
Here, I believe.