You could setup an enviroment variable in the scripts.ini file:
Then that enviroment variable could be set to wherever:
CorpWDIR = \\Host\folder\WDIR
at run time it is still interpreted as a UNC path, knew I was missing one of my examples of things I tried.
I just went through the exact same process you did, Andrew. Chaps me a bit that Mentor recommends the use of UNC paths with everything and they don't work with the script loading.
The solution is to add the path to your Scripts directory to the WDIR environment variable. It works.
edit - I thought it wasn't working but I had a bad path. It does work.