Tandem on the BART?

We're going to be driving down the coast for a week long tour in Sept that starts in SF. We had initially been told that parking would be available at the start, but now it turns out that the parking is at the airport and we need to figure out how to get to the start on BART with our tandem. Is it possible? I've read their rules for bikes, but it doesn't say anything about huge honkin monster tandems. Any advice? Any leads on long term parking near the Presidio area that doesn't cost an arm and a leg?