One thing the OP did not make clear: Is this a paid stay or is this an award stay. Award stays are not available for the Platinum override, in fact, if all of the standard rooms are sold out you can't even use a Stay Anytime award. In this case you are SOL. Sorry.

If it is a paid stay, I would challenge the hotel as to the reason the override is not available. It has been stated on this forum by "those in the know" that hotels must apply for exemption from the Platinum override if there is a special event. Of course, you have to pay the rack rate to use the override which could get expensive.