My friend and I played through most of the game as Peach and Luigi, and so ended up having to clear each level with Mario, Toad, and *COUGHCOUGH*. Since there were just the two of us and three characters left, this would mean we'd have to play through each stage twice more to completely clear it. And this didn't sound very appealing.
So instead we turned on another controller, and just had the character neither of us wanted (Mario) sit around in a bubble until the end, where one of us would guide him to the flagpole. My friend then figured that the easiest way to get Mario onto the flagpole at the end would be to pick him up and toss him. And this quickly escalated to us trying to carry Mario through each entire level, where we'd toss him into powerups, onto enemies' heads, and carry him through any floating stars. We treated it as though Mario were dying, and almost completely debilitated, but still wanted to go on one last adventure. And so we were granting his wish in any way we could, shouting words of encouragement as we went. "Way to go, Mario! You killed the boss!" "Nice one, Mario! You got the top of the flagpole!"
And it's all the better when he ends up winning in points.