The "Scripting Bridge" is a way to tie any language in to the Apple Event messaging architecture. I guess you can think of it as bridging Lua to Objc, but it is much more language agnostic than that. This is how you can have automation scripts on OS X writing in Ruby/Python/JavaScript/etc.
I get that your bridging is manual, but if you built on top of the scripting bridge you'd have something much more general, and your "manual" bridging could just be pure Lua code.