According to a PlugShare report, there are two Model S HPWC 80A and four 14-50Rs at the Tesla location at Montgomery Mall (and these are reserved spots only for Teslas).
Also, since you are going to probably top off at the Delaware Supercharger on your way down, it's only 96 miles from there to Chevy Chase. You can just plug into a standard 110V outlet at your Thanksgiving destination and charge at 3 mph, which should be more than enough to get you back to Delaware Supercharger with room to spare...right?