Were you ever able to get this figured out? We are having the same issue.
Unfortunately, no. We're going pay someone to write custom code to make this work.
It seems that SW team already knows about this issue...
Check this SPR602143:
"Enterprise variables mapped to a SolidWorks property with a value of $PRP:"SW-Configuration Name" incorrectly shows active configuration."
Didn´t got any answer from them.