I can't attend a huge wedding & reception tonight in which I RSVP'd yes weeks ago. Etiquette help needed!?

OK, here's the deal....it's Saturday afternoon now. The church wedding starts tonight at 6:30pm. Reception at an expensive historical reception hall thereafter w/ 300+ guests. Black tie optional, but it's NOT going to be a sit-down dinner. You know the bride is running around getting ready as we speak.....doesn't have time to receive my phone call to regret at the last minute. Who do you think I should appropriately contact? The coordinator at the reception hall? Should I send a telegram to the bride & groom at the reception hall? Should I write a note and drop it off at the reception hall with the coordinator? What's the appropriate etiquette for such a cirstance? Please.....I feel bad enough I must decline....cirstances out of my control....I want to do the right thing and decline graciously and respectfully.....any help would be sincerely appreciated. Thanks!