I'm suggesting adding new features to "Path manipulation" action. You can add "Convert to long file name" / "Convert to short file name" options and "Append relative path to absolute" / "Extract relative path from absolute" options. The last two options should contain additional parameter - "Current folder", which is used for resolution. User may either set it to real current directory or enter some other value, like "%FBPROJECTDIR%".
P.S. Take a look at PathGetLongName/PathGetShortName in JclFileUtils.pas.