I know this reply is too late, but for future reference, just head for the bus stops. Once there, you can walk straight into the Tube station via another entrance which has no queue.
Thanks - will keep this in mind for the next time around.
Have a similar problem this weekend - invited to a party at the Roof Gardens in Kensington and trying to plan how we will get out of the city at 0300. Looks like the cheapest solution (other than the night buses) is a pre-booked taxi