I know it's not the same thing, but we were able to negotiate a code rate that had expired at the GF. We had booked with last years fall room only code which expired in July or August for a September stay. When we were there, we asked about the possibility of staying another night at the same code rate and were told that would be OK subject to room availability.
This was handled by concierge, so it mightn't be the same as front desk, but she phoned up someone for us who okayed the rate. Unfortunately when she tried to get us a room the hotel was full except for main building concierge (I know she was telling the truth- there was a big conference on and we had been upgraded) which couldn't be discounted.
It was strange, when she was talking to the original person to okay the rate, he gave her a code to use for her computer- AB or BC or something, so I guess there is some sort of system in place to give 'on the day rates'.
Good Luck!