I'd put an anti-reflective filter in front of your flash... that should do the trick 
If you can use off-camera flash that will be your best bet at getting the ambience of the glass with usable pics of the people...
All I can say is best of luck to you 
Andrew Rodgers
Perfected Perspectives -- Photography by Andrew Rodgers | Andrew Rodgers (acedrew) on Twitter | Login | Facebook
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Canon 50D 24mm, 50mm, 100-400mm, 28-135mm
Panasonic Lumix TZ-3 Yeah, I have optical image stabilization and a 10X lens, it also fits in my pocket.
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