Well..., it depends on if the customer wants the stained glass to be visible with the same view in the frame from both sides.
If he is only looking to have the stained glass framed and mostly seen from the front, not a huge issue.
If he wants it to look exactly the same from both sides,...bigger issue.:icon9:
If he wants the frame to be the same on both sides, you would have to build the stained glass channel frame around the stained glass with many, many, many, cut and joined pieces with perfect angles and assembled around the glass.
If he is just mostly concerned about the front side, you might be able to find a ready made round frame if the size is available or you could make a "spandrel" frame that is rectangular on the outside but circular on the inside using a rectangular piece of wood that is cut in the center with a rabbet for the circle as a sort of mat and stained to match the outside rectangular frame.
Or, you would have to create and build your own moulding and frame with a channel from scratch and do the finishing.
Or, could it just be hung as a circle with a chain and without a frame?
Good luck on this one..
Keep us updated on what your solution is.
(it might just be to say "Yeah, I don't think so")