brake rotors don't "warp"... another long standing myth.
http://www.stoptech.com/whitepapers/...otors_myth.htm
the "warp" you feel is pad material burned onto the rotor from crappy pads.
Substitute blank rotors for the front and you'll be golden. BTW 240SX rear rotors are non-vented, and too thin to fit vents into them.