I'm afraid it is not possible to meet your needs; user highlighter can only define keywords and use predefined comment patterns (in general) so beside comment and four keyword groups there is no other way to (user) highlight your code.
If you point mr Fiala to exact specification of syntax of your language (and possibly some proof that there might be some relevant user base) he might be opened to implement it natively. -- <http://forum.pspad.com/read.php?2,59488,59492> PSPad freeware editor http://www.pspad.com
