Yeah, though its unlikely I'd use ".."
Since a source tree is usually multiple levels deep just using ".." isn't good enough (and it doesn't work for files in the root of the drive).
Consider the backup files to be something like *.O files produced during a build.
Placing foo.o in the same folder as foo.c is the easiest thing to do, but also has a lot of problems.
Maybe this could be project or workspace specific, but that is probably too complex.
A simple "%" substitution would do it.
The user could set their backup path to "%D\vsdelta".
"%D" is replaced with the drive/partition of the source file.
The most complicated part here for Slick though would be handling backup history split among several locations. Some of the locations come and go as the user adds and removes flash drives. Right now, its all in one place.
I don't use the non-history backup option, but as I was looking at these options today I was surprised how limited it is. I'd think that it would allow different backup naming conventions, and naming of the backup directory. Especially on Linux, using a dot prefix to the name of the backup file or directory would be nice.