I went thru the same pain. MP account as "Bob", credit card and driver's license say Robert. No problem until this year, when the TSA ticket checkers (I know they aren't TSA employees, but really) started having heartburn over the fact that my ID didn't have the EXACT same name as my ticket.

At first MP told me it required a written request, but after the 3rd time I purchased a ticket and had my MP number entered manually at the RCC (they can override the "first name match" requirement), an RCC angel at SFO was able to persuade MP to change my first name in real time. She did have to spend about 15 minutes on hold with MP, but there was no line at the time and she managed to make it happen somehow.

Bob