How to disable the ticket form dropdown?

Does anyone have some custom javascript that would allow me to disable the dropdown for form submission when someone lands on a specific form? I've tried everything but it seems like the from request drop down doesn't behave like a normal drop down.
I want this to be un-selectable when a user lands on a certain form. There a few hidden forms we send users to from time to time but if they click on the drop down, they can navigate out of that form and not be able to get back. Any help would be extremely appreciated!