I have no plans of doing this, but maybe I can inspire someone else by talking about how it would be done.
All of the game's cinematics are modifiable and stored in one of two places: "\script\slcinematic.lua" and the folder "\flash\".
Any full-screen 2D cinematics like the manga pages are created with flash and stored in the "flash" folder. Anyone who knows how to disassemble and modify flash files can easily add in some voice overs during any of these.
Everything else is controlled in the slcinematic.lua file. It moves the camera, creates NPCs, controls animations, and plays sound effects. The file acts almost exactly like a script to a play.
For example, the line:
Code:
LuaGlue_AddCNSound2D("TLQ\\TLQ3_2_Chichi.wav", 0.0)
Plays a sound of ChiChi running during TLQ3 (
as seen here). It should be possible to add additional lines to this file that play custom sound files.