My suggestion would be to trade in the 2004 Sport on a 2004.5 Wrangler Unlimited which is 15 inches longer. This will have both more legroom in the rear seat and usable storage space. They are taking orders for Unlimited's now.
I know this will ding your pocketbook, but there is no safe way to move the seat back - the seat belt and shoulder belt anchor points are designed into the tub and rollbar.
1967 Kaiser Commando
2001 Grand Cherokee WJ
2003 Wrangler Rubicon TJ