I tried this just this past weekend. Got 4 bags in decently. Take out the drivers and the two in the back can just hold onto them.
You gotta lay the bags in the cargo area, width-wise, 2 and 2... then you could just hold the drivers, or if you had the 40/20/40 split rears seats, you could just lay them up the middle.
It's tight, don't get me wrong, and there was no way I could see much out the back window.. but it works. and that's what side-view mirrors are for.