Linux-style path on windows or vice versa
NTFS supports symlinks, so you might be able link C:/x/,D:/x/ etc to X:/, and then you can omit the disk prefix and it will assume that you mean the current disk, find the symlink, and go look in X:/. Horribly cludgy, of course, but it's the best I can think of.
mklink /d C:\x X:\