1) Just rip up some junk mail and pack it in with a screwdriver until it's tight.
2)Install masking tape over the paper just below the the top of the boxso the tape is sticking to the side of the box thenn razor off the excess tape stick out.
3) glass over it.
4) drill hole after it dries and roter it out file the edge and your done.
In the second pic you can see that I slipped with the router ( not drilling a hole first).
I build my boxes from scratch