It drove me nuts for while when getting the mail, boat ramp, etc.
I slid the seat all the way forward and unplugged the connector at the seat belt buckle. Then I stripped a scrap of wire and cut off the bare strands and put a few in the plug to short the 2 terminals together and reconnected the plug. No more lights or dings because it thinks the belt is always buckled.
I do use my seatbelt, I just usually like to start up and get rolling and then put it on once I'm settled.