Add additional options to thread

Basically I want to be able to add permissions to allow an extra field to appear when creating a thread. There are lots of examples with permissions, so that's not a problem. My problem lies with adding additional fields to the create thread page.

controllerName:    XenForo_ControllerPublic_Forum
controllerAction:    CreateThread
viewName:    XenForo_ViewPublic_Thread_Create
contentTemplate:    thread_create
I see what's being called, but I can't figure out how to add in an additional field ... then IF the field appears and something is put into it, I don't know how to save that data.

I'm looking in XenForo_ControllerPublic_Forum at actionCreateThread() and actionAddThread().
Digging around a little more, I don't see a hook in the thread_create template around the thread_fields_status template include. I would really like to place it just under set thread status. The thread_fields_status template doesn't have a hook either.
I am able to hook into thread_create_fields_extra. While it's not ideal, it's all I have for the moment. I'd like to be able to hook into the fieldset just above the poll with Options and Set Thread Status.

Still working on how to get/set the additional field.