Perhaps a file-association could help with some trickery there.
I'm not on top of the xfce settings etc, but if it has problems parsing the args properly then you coudl wrpa it up in a script (so that it becomes a single executable, which in turn calls pndrun and the executable.)
Now all that aside, note there are two pnd_run's .. theres pnd_run the binary ("pnd_run"), which can run an app just fine; it'll find pnd_run.sh and set up the call for you, but it has some limits; its mostly for quick and dirty invocations. If you want more power over the run, use pnd_run.sh directly; a few more things need to be specified (such as the appdata name and such), but it gives you more flexibility, and has some good argument handling; note the '--' option which allows anything after the -- to be passed more literally to the pnd without being expanded by the pnd_run.sh handled; we needed it for properly handling arguments in the file-association thing.
Amnyway, I haven't thought at all, got 3 babies climbing me now, and give you 10secs only.. but you have multiple small challenges here.. i) figure out what xfce is doing when launching, and then ii) figure out how to invoke the pnd; you can do these separately. Get the pnd invocationw ith arguments working from the shell, so you know what to do; then get the xfce launchign bit going, calling the pndf as needed.
Sorry, gotta run .. I took a day off to watch babies so my wife could have a day of freedome; so I'm buried
jeff