This exact request was actually pro-actively given to me on a LGW - TPA in Y last year. My wife is ceoliac and had a GF special ordered, and the two kids had a childs meal ordered, with only me being "normal". A member of the crew came down before meal service to see who was sat where, and offered to bring me my choice of meal so we could all eat together.
I was mighty impressed I have to say, and saw this as being a benefit of choosing a decent airline. BA has it's many detractors, including me from time to time, but when they get it right it reminds me of why I choose them. Top customer service IMHO.
All that said, it does not mean that you will get the same treatment ! I took this to be the action of a single member of crew acting on their own initiative, but I reckon you could ask as to the possibility, but be prepared for a polite no.