You have to give it up for video game modders. Among other things, they're the ones who often help titles maximize their potential, or make things right. Like including extra features that were not originally included in the first place for whatever reason.
Take Super Mario 64 for example. There's a reason why it's not Super Mario Bros. 64, because it's a purely single player experience. Wouldn't it be nice if you could have a friend along for the ride? Well, now you can, thanks to a modder who goes by Skelux. Here's what it looks like in action:
Those interested in playing the hack can find download links and instructions as to how get everything working should consult the notes section of the YouTube video.
It might also be worth noting that the author has another hack in which all the levels are entirely custom designed by himself. More information on that can be found here.
And yes, it is rather perplexing that the second player doesn't have Luigi's color scheme.