It seems that there is no documentation for %WINDIR% which might work (not tested) but I found no equivalent of NSIS $SYSDIR which is required to portabilize many admin applications.
[Moved from PortableApps.com Platform support to Portable App Development forum - mod Chris]
It's just $SYSDIR in NSIS. So it's %SYSDIR% in PA.c Launcher, I believe. Most apps should not require things to be in SYSDIR and I doubt we'd approve an app if it did unless it was something really unique and useful. DLLs can usually just be in the working directory of the app.
Sometimes, the impossible can become possible, if you're awesome!