I will admit that I have very rarely, if ever, seen a hotel load CL room upgrades into the reservation tool. But I was able to help a friend (who wasn't a Gold/Plat elite) get an upgrade to a CL room using some extra awards. It all depends on the hotel management. They can pretty much take and do a lot of things...if they want to.

Back when the Bay Point Resort (Panama City Beach) was a Marriott resort, I worked a deal with the manager to get me 3 rooms, one with a suite by itself, the other two connecting suites and all for awards. I think I worked it by paying the 2 extra upgrade awards per night (an extra 10K per night) to get all three upgraded to the suites. (Note this was just before the summer season was ready to start, in May I think, which meant the manager was probably more willing to wheel and deal some. I did something similar many years ago at the Kauai Marriott resort (and at the time the manager threw in free breakfast for my wife and I as well.) ^

A lot of hotels won't probably budge much, but you never know whether they will or won't work with you until you ask.