[ ... ]
I've tried using envvars in the stunnel.conf (e.g., cert = %USERPROFILE%\usercert.pem), tried adjusting the command line to include "-p %USERPROFILE%\usercert.pem" as an option ...
We implemented something similar by simply making a "C:\stunnel" directory on each PC, naming the certificate the same thing on all machines, then hardcoding that path into the stunnel configuration (e.g. "C:\stunnel\usercert.pem"). Not quite as nice as %USERPROFILE%\usercert.pem, but it worked. :-)
Hope this is helpful,
----Scott.