Thanks to Eric Lippert we finally have a succinct definition of Mort (not to mention Elvis and Einstein):

the professional line-of-business programmer who lacks a degree in computer science but has a great deal of familiarity with Office and VBA, and who typically writes productivity applications shared amongst his coworkers.http://blogs.msdn.com/ericlippert/archive/2004/03/02/82840.aspx

Of course, I still maintain that Terry Pratchett was closer to the mark.