After two more ghost tailgate openings this weekend....guessing from fob in my pocket, I took the remote apart. There doesn't appear to be a way to easily disable the button on the little circuit board in the fob.
So, I carefully pulled the front rubber up on the fob. It's just pressed in and comes up easily. I put a couple drops of super glue on the little mechanical button under the rubber. I then let it dry completely for 24 hours. The tailgate release button is now hard as a rock and there's not a way to accidentally hit it while driving.
I'm certainly not recommending this permanent resolution to anyone but sharing a super simple fix to disable the useless function on the key fob. I for one am tired of arriving to a location only to find I've been driving with tailgate down. My Ford was the same.