Rather than casting Fly all the time, the party mage could always make Boots of Flying for everyone.
Yeah, this was my thought as well. If the party thought having the Fighter fly was that important, what was the reason for not trying to find or acquire a magic item to let him fly on his own so the wizard wasn't expected to always cast the spell?
Obviously, the DM doesn't have to make an item like that available to the party... but if the DM knows the spellcaster is unhappy with the game because this is an expected part of his job, then you'd hope he/she would acquiesce a little.