Major thanks to those that commented here, and my TwitterVerse, who came through for me big time. In particular, Joel Ross pimped my ride and hooked me up with a solution that honestly just never crossed my mind at all (i'm not a web guy...wtf is httpcontext?) but took all of 5 minutes to implement.

He posted the solution here on his blog, so go take a read. This was actually the second solution he posed to me which, in my sleep deprivation I didn't really grok at first, so I went with the first solution he emailed me.  Basically what it amounted to was making a reference to System.Web in the existing static config class, then pulling from HttpContext.Current if it wasn't null to grab a session variable, otherwise it would operate as it always had for the WinForms apps that reference it. 

This solution is not pure I know, I have the System.Web dependency, yadda yadda yadda.  Don't care. Didn't have to change any application in production currently, made one change to one class that had zero upstream repercussions (remember there's 200+ other classes calling this thing), and it got the job done.  Sometimes that's exactly what you need. I'll probably refactor later to remove the System.Web dependency but for now I've got other fish to fry.

Anyway...big thanks again to Joel, I really appreciated it.