You can retain your wheel setup if you drill the b15 stuff to 4x100, but you do lose your brake setup.
The info about hybrid axles is sprinkled in some build threads. Coheeds, Ashton?, mine. (ashton has at least two build threads)
The problem with it is finding b13 and b15 axles that use the same spline type mid shafts.
I've come to the conclusion that I want to keep my wheels and i dont care about getting different brakes, even though I wont be able to use the 13" drag slick setup that I already bought. Right now mine has become more of a daily since my wife wrecked my cobalt last week. But I dont have time to go find B15 brakes/spindles in a junkyard.