There are a couple of forum topics that explain the data files, their extraction, z-buffer images and tools for creating 3D scenes from them:
viewtopic.php?f=26&t=15537&sid=8ba5dbad ... a627b80aba
Some scenes have alternative angles which give more complete image of the surroundings that is being cut off by 4:3 aspect ratio. The "Z-buffer to 3D" can be used with multiple scenes to give an exact geometry compiled from multiple angles, alongside with texture projecting to give an almost complete 3D textured "room".
Some scenes have unused angles, which can be accessed by extracting the game files. While others have "cutscene only" alternative angles, like the Manny vs Domino in front of Membrilo's morgue, which can be switched during gameplay using the "developer commands".
Some scenes are "video" only, like the Calavera caffe cactus or the Rubacava Automat which can be seen from different angles only in a video (which has no z-buffer dara and the original game has heavy video compression artifacts).
And some scenes like Land of the Living Diner have no references at all.
But in the end it all boils down to Photoshop
You need the original scene and then use whatever technique you like to "draw" the widescreen addons. You can use zbm2obj to recreate the room in 3d in widescreen. You can just "clone" existing parts of the 2D image to fill in the blanks.
Note: different angles mean that some objects are obscured, so there are elements that need to be made from scratch
Thanks. Here are some of the screens that had all of the mentioned "techniques":