I have a similar request but for a different reason. I'm about to move around 15,000 images over to LR4 from Aperture. Many of the earlier images are scanned from film JPG masters with minor edits. Starting once I got a camera that did RAW, I have all RAW files. I know I can't move the adjustments over, but what I would like to do is have the file pairs be such that the edited JPG is what is shown, but I have the option to go back to the original RAW or JPG if I want to start over with edits. Normally, I wouldn't do that, but I do occassionaly go back and redo a photo if I get a new tool, or I learn a new technique that could improve it.
Aperture provides a way to swap which file is the master (use JPG as master or use RAW as master). Does LR4 have something similar?
Since some of my files are JPG master + JPG edits, am I limited to the stack approach?
Is there a better way?
Note, I really would rather not keep everything in Aperture around because I'm guessing that will end up causing me headaches if I change things somewhere.