[mr.maroonsalty]

I'd do it with a circular saw and a diamond blade with plenty of water. I would drill small relief holes at the beginning and end of the cut. The saw is then left with the depth lock open and is allowed to slowly enter the cut, plunging, then is locked down right at full penetration, so not to wonder or bind. You will have to decide if cutting the trim away is a structural risk worth taking. Another way of doing this is with diamond dremmel type tool: again with plenty of water, working wet and slowly you can etch your way through working the entire cut little by little through the glass.

This is the do it your self section; it seems people have missed that point. Like any do it yourself project things sometimes go wrong. If you are not comfortable working with tools please don't attempt doing things like this. $10k glass cutting tools have not been around as long as glass which people started cutting very thick peices of into intricate shapes long before UNCLE was born. Maybe research how glass was cut in a mid evil or gothic cathedral. I'm sure there are other ways than the ones I described.