yeah you sure can hook it up to stock... its pretty easy to do, but its even easier with an aftermarket hu and you will get WAY better sound.. trust me i know cause i used to have subs connected to the stock hu
to get to the hu just remove the trim from around it, you can just pry it off with a flathead screw driver from the top. then there is i believe 3 bolts around the hu you remove, then it pulls right out... to make it easier, you may want to remove the shifter so you have more room and can move the trim peice out of the way..
oh.. and you will have to tap into the rear speaker wires.. you can get a diagram showing which is the rear speakers and which is + and - from
www.the12volt.com i'm not sure what they are off hand.