I tried this fix myself,and while it DOES fix letterboxing during gameplay. It should be noted however that ALL 2D UI elements and FMVs will be reverse anamorphically stretched now.
The game will still use 16:9 menus and assets but squished (Reverse Anam.) to 4:3 , the "Original" 4:3 setting will also result in the 4:3 FMVs being used, but since these are actually encoded in 1440x1080 space within a 1920x1080 video. It results in the same RA
Ex gameplay screenshot
http://i.minus.com/iXBu6kbwiLOT1.png
Ex FMV screenshot
http://i.minus.com/iLVV6htmbf7oE.png
Ex UI/2D element screenshot
http://i.minus.com/ibcsZACxwTVnAz.png
http://i.minus.com/iBL2qfILBFiZw.png