We’ve been having a good old time with this over on the Pocket Knife community, but I figure there’s probably a lot of crossover with this crowd as well.
I’m sure you’ve seen various clever little one piece utility knife blade holders on Thingiverse and so forth, and while they’re quite functional I don’t think they’re nearly as overwrought or silly enough, nor require quite enough components.
Rather than repeat my entire post from there over here, I’ll leave you with these:
Link to .STL Files And Assembly Instructions
From what it looks like you can slide it in and lock it with these two pins on top. Not sure how safe that is but considering we’re talking about a makeshift balisong, safety can’t be your main concern