I agree that it's kind of dirty, particularly since it's basically a bug. I think making cars in the corridor impossible to get back into would help, since then a blocking car would actually respawn and give people an opportunity to get in. I do mean only cars, bikes and other vehicles that can't block the corridor should be unaffected. Maybe decreasing the respawn time would be a next step. Just a block of less than a minute can be effective. If people really miss being able to block off the entrance, maybe a one-time (per presidency) physical block of a minute or so, activated by only the President, would be cool. Make it so people can still shoot through so the "firefight through a narrow window" aspect is retained. Maybe a door that comes halfway up from the floor.
Those who are complaining about terrorist Hydras need to actually do something about it. The police/swat class can be the most effective protecting force in NSA, if it's made up of non-idiots. I often end up stopping many of the terrorists from even getting near the President (that includes the ones in Hydras), whether or not he's in Area 69. Two or three reasonable competent police could make it impossible for anyone to get near on the ground, and for anyone to get near from the air by taking over the airports. Before any of you give me the "but I can't fly" bullshit, try learning. I couldn't fly either, at one point.
Also, the Hydra excuse is only half-relevant. This tactic can also be used in WV, which has a much larger Presidential margin for error and therefore little justification for its use.