>I want to post something in the 3rd-parties forum, but see that in order to do that I have to change my settings first so it will show up in the dropdown. I don't want to do this. I just want to post it and get a reply. I don't normally want to see that forum on my main page, but do want to see it when creating a new post. I'm spit-out-of-luck, aren't I?

Yup. But if you set it temporarily, to be able to write your message, then set it back, I'd bet that your reply(s) will be viewable by you regardless.