Can you rewrite some parts? Maybe shift the melody around to a stronger section when necessary? Maybe make cuts in the piece? We just did our "christmas concert" and only one piece was a true holiday piece, so maybe pull out a stand tune that they liked but make it sound like a concert band instead of a marching band
Individual playing is a winner, so is being SUPER positive about anything that is correct. Sometimes we focus so much on what is wrong/needs fixing that we gloss over what is good/improved.
If none of that works maybe you can bribe them with candy or stickers!