http://store.clubgp.com/itemview.asp?itemid=59

The SoundGate GMSW1 lets you retain the use of the factory steering-wheel audio controls on late model General Motors vehicles when installing any SONY RM-X2S or RM-X4S compatible receiver or CD player (including the SONY ES product line)! This is a hard wired solution and does not require an infrared remote control

95$ or so there, there probably can be found better prices...