Okay, those links help hugely!
I think you can do this as an original, and call it a request by the creator of the OC. He seems to love having people write using his characters, and you can certainly tell that he's aware of us over here.
The safest thing all around from our point of view here is to keep a record of his permission. I can take that via an email from him, a quick one liner referencing your pen name, the character name, and his okay for you to use them. If he's more comfortable doing it via comments on H-F, link me and I can take a screenshot to show that he was aware of you using his character and approved of it. The "Thans for the story, I'll go read it" sort of thing certainly shows that he's aware and approves.
The fake brands and such comes only if the usage is a central feature. Obviously, if you mention a person grabbing a cup of coffee at Starbucks, and then don't talk about Starbucks again, it's not disclaimer-worthy, and for the most part, constitutes a bit of free advertising for that chain. What gets touchier is if you have an ongoing reference, such as a character like Superman making an actual appearance. Saying someone is "...acting like Superman, for fuck's sake!" is not something you should need to disclaim, though. If that makes it clearer than the usual mud I toss out there.