There's your problem in a nutshell. There is no way to legally transport firearms into DC (unless yu are a DC resident, have jumped through all the hoops, and have the necessary paperwork).
I'm going to throw out a fairly screwball idea: On a certain day an unexplained coincidence takes place in which a number of persons, all acting on individual initiative and not in concert with any other person or group, takes a walk from Long Bridge Park in Virginia to the foot/bike path of the George Washingtom Parkway in DC, then to Washington Blvd in Virginia, then down Boundary Channel Drive back to the starting point. In Virginia loaded firearms can legally be open carried[SUP]1[/SUP]. At the DC border all firearms and ammo are unloaded and placed in locked containers, as per FOPA. Firearms are then carried, per FOPA[SUP]2[/SUP], through DC[SUP]3[/SUP] to the Virginia border where they can legally be removed from the locked containers, loaded, and openly carried again.
Please try to punch holes in this. If you do not like my "unorganized" hypothesis, then let's get a permit from NPS for a group walk on the GW Parkway, and from Arlington County for the hike back to Long Bridge Park along the public sidewalk. Admittedly at that point there would have to be a "person in charge" which takes some of the fun out of things.
stay safe.
[SUP]1[/SUP] - see
http://leg1.state.va.us/cgi-bin/legp504.exe?000+cod+18.2-287.4 A firearm would be illegal (loaded or unloaded) unless the person carrying it had a concealed handgun permit. (Case law does not address if a concealed carry license/permit from another state would be valid.
caveat emptor and all that.)
[SUP]2[/SUP] - FOPA provides that persons traveling from one place to another cannot be incarcerated for a firearms offense in a state that has strict gun control laws if the traveler is just passing through (short stops for food and gas), provided that the firearms and ammunition are not immediately accessible, that the firearms are unloaded and, in the case of a vehicle without a compartment separate from the driver’s compartment, the firearms are located in a locked container.
[SUP]3[/SUP] - As participants would be walking, there would be no way to place the locked container in a trunk or any other part of a vehicle. Let the DC police scratch their heads about that.