I just got back from a short 10 day vacation, sorry to hear about the projector Mike,
as for a way to prevent the glass from releasing I would guess that putting a metal bar or set maybe three metal stops on the deep side of the vat would prevent the glass from moving in the xy position on the release cycle. most likely there is no need to hold it down in the z as we shouldn't see any upward pull of the glass from the cured resin.
So one way to do this that comes to mind would be to use some basic self tapping metal screws with gaskets. drill the appropriate holes and use a hex head like shown here. I would grind off the rounded bottom or find some that are just the bolt head then remove the excess under the vat of course. you could use the glass as a template for the the straight edge needed and then just mark the 3 or 4 holes along the line and drill. use a silicone seal or some locktite on the threads and the squared edge of the bolt could hold the glass in place prior to epoxying or silconing in the glass.