We typically render our glass seperately from the main building to give us more control with reflections in Photoshop.
This involves rendering the building without glass, and then rendering the building with glass, but with the glass objects having a 100% reflective (no falloff) and 100% opaque black in colour (ie no transparency).
We then render a multimatte ID on the glass so we can extract just the glass elements in Photoshop and adjust the transparency etc in post.
We also use the Rendermask script to render out an ‘environment reflection matte’ for the glass. This helps us have only the reflections visible in photoshop (without any vraysky etc) and then we can replace the reflected sky with something more interesting than the vraysky.
Would it be possible to add a render element for the environment reflection matte (ERM)? I guess you would choose which objects you want an ERM for.