Even though Payless is off-airport, they're on the way to Disney, not out of your way.
Their shuttle (or a competitor's rental car) takes you out the north airport exit and left at the first light (Frontage). Payless is less than a mile down on the right. Leaving Payless' lot with your rental turn right instead of their suggested left (or just whiz by with a competitor's rental). Less than a mile is next light (Conway), here take a left and immediately another left to get on 528 (Beach Line). Then take I-4 west (southwest) to Disney.
End of your vacation, sadly, take I-4 east to 528 east. Get off 528 at its exit 9 (Tradeport). Left and cross under. Nice cheap gas station right here. Get into middle lane facing north (with 528 crossing over in your rear view mirror). Required right onto McCoy, Payless is on the left. Their shuttle (or a competitor's rental) takes you further east less than a mile to 436 (Semoran). Right to get to airport north entrance.
Total toll, a dollar each way. At the toll plaza on 528 slow down and watch for the cash lanes (I think these are moved to the far right) if you are not familiar with the area and don't have a Florida electronic toll tag. Toll tags from other states (such as EZ-Pass, I-Zoom, Fast Lane) are not honored.
Disney hints:
http://www.cockam.com/disney.htm
Been there done that several times, have had no problems with Payless.