According to the SEP SBE Administrator's Guide:
The accepted formats for a File exclusion path include:
■ [drive letter]:\path\filename
■ [path_macro]\path\filename
■ Wildcards and trailing "\" are not accepted
That last rule means that you cannot use this format: C:\*\file.exe
If you want to specifically exclude a file, you must specify location.
And I have to question, if you need to exclude a UNC, how is it that you cannot map that path? What, exactly, is preventing you from doing so?