Service Catalog: Need to have option for Requester to set Item, but NOT the Category or Subcat

I'm in the process of building out our Service Catalog, and I'm building the simplest of forms for problems with a mouse or keyboard. With a bunch of coffee drinkers who like to spill coffee onto keyboards for some reason and mice that have issues, it's a high ticket generator. Anyway as I build out the catalog I want to assign a Category, Subcategory, and Item to the ticket. Our end users don't want to wade through the Categories, and they will get lost in our Subcategories, so I want to lock those in for them. But when it comes to Items...I have keyboard, mouse, scanner, etc listed and I want them to be able to choose which one is giving them trouble.

But I can't. If I enable "Requester can set" on the Item, it enables it for the Cat and Subcat too. Not what we want. I need a finer level of control than what the product is giving me today. I see SDP as a framework, and the more control I can have over setting where fields are displayed....the better.

On a sidenote, I'm also wishing I could ditch the description box, or be able to do more with it. Sometimes we just don't need it...or I want to simply put a message in there and direct the user to the resources I added...it saves me from getting tickets with simply the word "help" in the description box. (Yes, I know, it's pathetic, but end users these days want it short and simple.). But right now I keep bumping into these hard coded things that were set by Manage Engine...and it's really annoying. I'm not sure what can be done...but it never hurts to ask.