I agree with Tom Reddick and Anton. If you can, find a bottle with brand name appeal to the audience in question. Silver Oak, Dom, Veuve, Cakebread, Opus, etc.
But you’re probably looking to donate from your cellar and not go buy something like that, so see if you have something you can sell with a shelf talker. One time, I put together two WS WOTY bottles as an auction lot, printed out things from the WS site showing that, and they got a pretty good price.
Certainly, selling here and donating the money is the most sure way to get FMV, but I understand that the auction is part of the event, more than just writing them a check. The auction is part of the reason people buy tickets, attend and donate further. So you understandably want to participate in that rather than just auctioning the bottle elsewhere and handing over the proceeds.
If you don’t have anything that is going to realize good value from the audience and don’t want to buy something for that purpose, I would suggest that you put your good bottle up for auction (augmented by any shelf talker you can create for it - “97 points from Robert Parker” or whatever, no matter how distasteful that would be to you in other circumstances), and find another buyer who will value it properly (maybe someone from here, or someone from one of your wine groups), and have someone bid up to that amount as a proxy. For example, Chris Seiber is willing to pay the $300 the bottle is worth and we have a handshake deal before the event, you let people bid on it during the auction, but as you get close to the end, you put the name of your spouse, a friend at the event, whoever at $300, that person buys the bottle, Chris pays you back, etc.
That way, you’ve supported the event and the auction, the charity gets $300 instead of the $180 it was otherwise going to get, and everyone wins (except the guy hoping to steal the bottle for $180). It’s definitely more effort, though.