The Brain Exploder makes some custom products for airsoft guns using 3D Printing Technology and he has ready to be printed out and delivered to you is the Airsoft Shotgun Rail Adapter... "New addition to my Shapeways store is the Dual Rail Adapter that easily slides on and locks in place with no tools on to the popular and inexpensive spring powered airsoft shotguns by UTG, Bravo or Double Eagle. This allows for mounting of flashlights, lasers and cameras.

The mount has been designed so a light mounted on the left hand side will clear the slide and will still put the light to where the user can reach it while maintaining a positive grip on the pump. Alternatively the rail on either side can be used to mount a fixed light and run a remote line to the pump or top of the barrel for access from either side.

The mount does not get in the way of the iron sights, adds minimal weight and makes the shotgun much more flexible in terms of accessories.

Also let me know if you want to see this sort of mount of any other systems out there like Tokyo Marui, G&P..."