Apparently that's what somebody already did to mine. I ripped off the passenger side kick panel and found both the wires from the speakers there along with the antenna (traced both the wire bundle and the antenna back to the rear when I ran the wire up from there to the front for my Music Keg). Dunno what they were doing there, as they were long enough to reach up to where the radio mounts, but it saved me pulling off the rear quarter for the time being (until I get around to hooking up the sub).
Strangest thing, on the end of the speaker wires there was a plug which looked EXACTLY like the one that plugs into the back of my Kenwood, but it wasn't wired the same. Not taking any chances, I clipped it off and wired in the plug that came with the Kenwood. I've still got no idea what those other two plugs behind the dash are (though I'm pretty sure one is from the CD changer in the console). I just wired in the standard grey connector from the Scosche kit, and wired the speakers directly to the kenwood connector, turned it on, and it worked.
I left the RCA jacks from the Kenwood for the Sub input and Aux input hanging down where I can reach them from the glove compartment, so I can hook them up later without ripping out the radio.