A glory hole is what happens when there's a hole that a dick wants to go through or an ass or mouth wants to nestle up against hoping for a dick. But why limit yourself to a toilet stall or what you can carve out of wood and install in your backyard shed? You've got a portable glory hole and it's called your pants, more specifically your zipper. Or what's created if you purposely split the seat of your jeans, dress pants or mascot costume.
As for the not being able to see the other guy part, just turn your back to him or close your eyes. Or only stare at the parts of him you'd see through a traditional glory hole, like his dick, balls, ass or, I dunno, the Wall Street Journal he was pretending to read while waiting for Mr. Right to find him through the 4" diameter hole.
Pro tip: to determine the area of the glory hole, multiply the diameter times pi.
So here's a couple vids involving pants gloryholes (click each pic to open the clips on Le Tube de X). Heads up that the first video has an obnoxious dance song with the lyric: "Tonight I'm fucking you." I'm hoping it's Ricky Martin's next single.