They should have the bus route changed to not go on the federal property - just "next to it". Then, the feds can shuttle everybody back and forth.
that's the obvious thought on how to solve this, problem is I don't think it's that simple. Not knowing the geography, alternate routes, number of people who may get disembark at the Fed facility from that bus, if any, etc...
In DC the Metro goes through a number of areas that are restricted, (Pentagon) and of course there is not an option to build a line a couple of hundred feet outside the area.