I just went through a similar excercise. I still have 30-50% left on my brakes but pulled the trigger on a BBK 2 weeks ago. I will put the old brakes back on when I sell my car next summer then sell the BBK as a part out.
I think there are a couple of options.
Wait until the brakes are finished and go the OEM replacement route at approximately $2,000.
Remove the OE brakes early, store them, and replace with BBK. When your ready to get rid of the car, pull the BBK off as a part out, replace with the OE brakes. Then sell the BBK for hopefully less than a $2000 loss from the brand new price.
It ties up a little cash, but it is an option for similar or possibly less outlay.
At least that's how I rationalized it!
ESS VT1 6MT E92 ///M3