I also used electrical tape until I purchased a devise called Farrsight. I purchased it from Brownell's for about $11.00. Not sure if they still have them. You can google farrsight and get info. It is a disc with various sized holes that rotate to line up for your eye and has a clip to fasten it to your glasses. It can flip out of the way when not in use. Clip on sunglasses would also work. A friend used a strip of aluminum from a beer can with a hole punched in it and the ends bent over to attach to his glasses. He later bought a Merrit sight.
