The California Energy Code requires A/B switching in rooms over 100 square ft. in area, so this is a very common wiring scenario that Revit lacks! This is usually done within each light fixture. For example, a 3 lamp fixture will have the two outer lamps on switch 'a' and the center lamp on switch 'b'. This allows for uniform reduction in light level in the room and is missing from Revit MEP. In the case of 2 lamp fixtures, the switching pattern in the room is usually by alternating fixtures.
We need the ability to connect two switches to a light fixture. I guess we can just fake it for now but there has to be a large demand out there for this and I can't believe it is missing!