I am also from the area and spend entirely too much time at that mall. There's a really nice open meeting area just outside the B&N on the first floor between the Gordon Biersch, Coastal Flats, and another restaurant that just opened who's name escapes me at this moment. The TGI Friday's is in the same area as the theater on the 3rd floor about 5 minutes walk from the B&N and is also next to a large open meeting area (although it tends to be filled with kids and their parents as there is a play area nearby) and one of the large food courts in the mall. Both of those would be easy places to meet up and I am fairly sure that they wouldn't mind having us hang out and game for a bit as long as we are also buying food etc. (obviously calling to ask is a good idea). After the signing, as has been mentioned, there are a large number of very good restaurants in the area (15 minute drive or less) including several in "Tysons II" which is a different mall just across the road.
Short version, there's a lot of options, once a head count exists someone (it would appear to be SkinsFan since I'm not about to fight him\her for it) can call around and see which of the many places would be willing to work with us to hang out before and\or after the signing. But the head count is probably the most important part.