Kevan:
You should be able to do this with the Floor Plan Cut Plane (I tested in AC19, I think AC15 has the same options). Set the Beams to Show on Stories:
Home & One Story Down (Home Story is the upper floor), Floor Plan Display:
Projected with Overhead, Show Projection:
Entire Element, Uncut Lines:
Solid, Overhead Lines:
Dashed. For the upper Floor, set the Floor Plane Cut Plane to be completely above the Beams, for the lower Floor, completely below the Beams. The Floor Plan Cut Plane is stored with the View, so make sure it is set correctly for each View that shows the Beams.
David