Thanks for the response. I guess it would be really just a "nice to have" to have the paths relative. I will simply work like DeCarlo suggested.
The main reason I was wondering if it's possible is because I am working with a lot of animated textures (jpg sequences) and I wanted to have a clean & portable folder structure. I think there is an option to "collect files" when done, to make the project portable, but I am guessing that would just copy all my video textures to a new folder. Since they are quite large I don't want to have them twice.
Anyway, simply moving old versions of the scene file to a backup folder does the trick.