Ahhhh, Litle Framer I see by your by-line that you were a Matboard rep...
Did you refuse the job because "they wanted it cheaply done" or because they wouldn't use a mat!
2400, do a search this topic comes up a lot. We usually recommend running away from these jobs, or if you are determined to do it then keeping it away from the glass by matting it on both sides, preferably with 8 ply for strength to stand up.
When I have been asked to do this the customer is usually happy with getting the back photocopied and either framed on its own or attached to the outside of the frame on the back. While a customer may want the option to take the frame of the wall they typically won't want to handle it after it has been put up on the wall. Way too much hassle to do everyday.
So, you could sell them two matching frames, with a wide selection to choose from, and give them the piece of mind of not worrying about dropping and breaking the glass just so they can show off the "back" of the original. In the long run they will be happier, and be able to see what they wanted, and the original will be better protected.
Just some random thoughts to think about.
As a further selling point, if you present both options and show that they will cost approximately the same, due to the extra glass, mat and labor charges then the two frames will sell themselves.