I think this was discussed somewhere else on the forum, not sure where atm.
The problem is, is that the Help Topic is used as a routing tool to a department and not an actual category. The help topic ID isn't even stored when the ticket is created.
To add this functionality you would need to (rough):
Add helptopicID to ost_ticket table in DB
Edit class.ticket to add the new var in all the $sql statements
add get functions to look up the Help Topic name based on ID
Then add the html/php to spit it back out.
I plan on doing this mod, just don't know when.