Hey, if you're going to try the old double mash, why not make a real old-timey day of it? Old English brewers, aware that, in the days before sparging, they were leaving a lot of sugar in the grains, would regularly (after running the wort into the kettle) "cap" the mash with another 20% or so fresh malt, and mash again for a small(er) beer. Surely they'd have done that after running off the second wort of a double!