Agree with making a note that you'd appreciate a Platinum (Gold) upgrade if one is available, please.

At front desk, if I really want one (I often don't bother if it's a short visit with lots of meetings and I'll use the room mainly to sleep), I'll ask when they start to write out the room slip, "Did the Platinum upgrade clear?" If the answer is not an immediate, "Yes", on more than one occasion that question has resulted in the front desk associate going back into the computer and saying something like, "Yes, I think we can do that."