There's no need for a project, this is already done for us!
Open up devmode, and load 6-1, replace 1 with whatever level you want from the end, add an x at the end for dark world, or load bonus1-1, same thing as before, for the cotton alley.
If you want to know all of the levels you can load (any warpzone can be loaded too), just look at this thread: http://forums.steampowered.com/forums/showthread.php?t=1656778&highlight=devmode
(Big thanks to keeblur for posting this nice list for everyone!
The only thing that might happen is, when the editor rolls around, this functionality might go away, so if anything, we could just go into each character exclusive level, save it in a folder, and zip it up just in case.