I'm not wotking operationally at the moment and I must claim ignorance of the fuel problems that started this thread but I would offer the thought that when I was talking to aeroplanes I rarely knew what was in the RMK section of a FPL. It relied on good support staff to pick out the info and, more importantly, get it to the controllers along the route. I would guess a general RMK on many FPLs would not get much action. And anyway, the vast majority of flights are on RPLs so RMKs specific to a particular flight are not possible.
The best solution to a general problem is for the operator to contact ATC management....but, as 055166k might be illustrating, management are not very good at passing such messages on!