Totally, rarely does anything key correctly through an entire scene.
1) Duplicate the layer
2) On layer 1 create a rough, tracked, mask around your people. Key the greenscreen that's left around them
3) On layer 2, create a mask around the glass and key it separately, you'll need to be a lot more gentle with the settings.
If the subject and the glass cross at any point, you may need to do some rotoscoping, but I think anyone would be hard pressed to say you could do this with one key.
Angelo Lorenzo
Fallen Empire Digital Production Services - Los Angeles
RED transcoding, on-set DIT, and RED Epic rental services
Fallen Empire - The Blog
A blog dedicated to filmmaking, the RED workflow, and DIT tips and tricks