So after a lot of prototyping and reading and discussion, I've come up with a plan for moving forward with my compiler project. I think I've come up with a workable compromise amongst simplicity, elegance, efficiency, and flexibility. I just published a writeup of my thoughts and the reasons behind my decisions, in case anyone is interested. (I don't make any ad money off click-throughs, so I don't feel bad posting here.)
TL;DR: I'm gonna be manipulating the lua stack /varargs in the main thread, and changing how I compile / generate code to match.