Hi
I am not sure if I understand you correctly, but I guess you want option groups (
http://www.w3schools.com/tags/tag_optgroup.asp ). I think this is not possible using HESK without tweaking the code itself.
The idea though sounds pretty nice.
But wait - before you spend to much time tweaking, consider using pop3/email piping. I thought the web frontend is nice - at first. Now users have not used the web frontend once, but only email directly to the helpdesk.
Olaf