Lots of questions today.
Please be patience with the rookie

Our service set is not that large, but it's quite complete for an IT servicedesk. It contains services and subservices. Here it is on Customer.pl New Ticket form:
It's in portuguese, but you get the idea.
The service highlighted in orange is the parent service. In reality, it's not reeeealy a service, for my IT department. It's there just to allow me to have a selection of subservices, which are the real requests. Users are supposed to choose only the subservices, not the parent service. So, I want the parent service displayed but greyed out, non-clickable.
I tried setting the parent service as invalid and maintaining the child services as valid, but this backfired - all subservices below the invalid parent service were not displayed anymore.
Can't think of anything else to try. My repertoire only goes that far.
Is there a way to do that, I mean, show a parent service but prevent users from selecting it, only its children?
Any help would be appreciated, thanks!