Really? I'd be curious to see how someone implements this. From my admittedly limited knowledge of the space, I see three different ways to tackling this. First, build out your own reservation system that uses your custom software to link the reservation system to the website and provide a vertical stack. Second, build plugins/hooks for existing electronic reservation/seating systems currently in use. Or third, work with the OpenTable's API.

OpenTable doesn't really have an official API. Urbanspoon has been touting Rez as an alternative but same story there. Will definitely let you know when we're ready for primetime.