Hide drop-down menu of help topics in new ticket

Hi everyone,
I'm testing osticket awesome and I have a challenge to solve.
We are planning to use the system to manage various types of help topics, some public, others private, and others that should be able to be created from the end-user frontend, but that should not be available to the general public but to a select group.
I understand that I can create direct links to certain help topics using the following modifier in the url:

open.php? topicId = xxx

where xxx refers to the internal id of the help topic.
So far so good, the problem is that I would like to use these types of links to give access to certain help topics for a small group of people, but without the rest of the people finding that help topic available in the drop-down menu at time to create a new ticket.

I tried to turn it into an internal help issue, but I lose public access.
I thought about completely hiding the dropdown menu, but that would leave end users without the options to choose which help topics I want to be public.

Anyone have an idea if it could be made that somehow public help topics exist but not listed, or hide some public help topic.
I would need them to be created by end users / clients, but not available to everyone, but to those who have the link that refers to that particular help topic.

Sorry for my poor English, I am a Spanish speaker.
I hope someone can help me with this.

Greetings!
Mauro