Found this and tried it. It worked. Hate the dinger. Love the trick.
2008 F250
Preparation
Apply the parking brake before deactivating/activating the belt minder.[/ol]
Place the gear selector lever in PARK or NEUTRAL (manual transaxle).[/ol]
Place the ignition switch in the OFF position.[/ol]
Close all the vehicle doors.[/ol]
Unbuckle the driver safety belt.[/ol]
Place the parking lamps/headlamps switch in the OFF position.[/ol]
Deactivating/Activating
Turn the ignition switch to the RUN position. (Do not start the engine.)[/ol]
Wait until the safety belt warning lamp turns off (approximately 1 to 2 minutes).[/ol]
3. NOTE: Steps 3 must be completed within 50 seconds after the safety belt warning indicator turns off.
For seating position being disabled, at a moderate speed, buckle then unbuckle the safety belt 9 times, ending with the safety belt in the unbuckled state. After this step, the air bar warning indicator illuminates for 3 seconds.
Within 10 seconds after the air bar warning indicator turns off, at a moderate speed, buckle then unbuckle the safety belt.
This disables the safety belt minder feature for that seating position, if it is currently enabled. As confirmation, the air bar warning indicator flashes 4 times per second for 3 seconds.
This enables the safety belt minder feature for that seating position, if it is currently disabled. As confirmation, the air bag warning indicator flashes 4 times per second for 3 seconds followed by another flash sequence of 4 times per second for 3 seconds.[/ul][/ol]
After confirmation, the deactivation/activation procedure is complete.[/ol]