Per a conversation with support, KB - http://www.symantec.com/docs/TECH106068, and built in Help Screen, the options are fairly limited and not exactly clear for the Symantec Variables.
It would be preferable to have native support of pre-exisiting default Windows Variables. This would provide a more robust and dynamic application of exclusions. It would eliminate any confusin in attempting to convert from a given Windows variable to a Symantec variable and building a sense of trust in the exclusion actually working.
It would also bring a more general synergy to the SEP product as a whole. In the Install guide, pg 516, it mentions that Windows variables can be used in Application and Device Control configurations. Why have two seperate variable classes? " The name can also include environment variables such as
%ProgramFiles% to represent the location of your Program Files directory or %windir% for the Windows installation directory."