Being the smart-a$$ I am, I'd have had to run with that ball.....
"Well, you see Mr. Distiquished Senator, we've already accounted for the additional weight of the personnel and vehicles on the island with Foundational Undersea Buoyancy Adding Rigs (F.U.B.A.R.'s) for such an event. As the population increases and decreases, hot air expelled from areas such as this building can be added to provide additional buoyancy as needed. When military personnel leaves the island, pressure can be releived by the use of a needle valve located somewhere near your cerebral cortex."