How well do you know your dentist ?
The dental Xray films have a lead backing which stops the Xrays falling out the back and scattering round the patient.
These can be flattened and wrapped round the tube. High quality wine used to have lead foil round the cork, mind you thet used to have cork as well. Now all I can afford is screw tops!!!
A touch of Super Glue usually holds the foil in place then tie the fly as normal.
Hope this helps.
Good wishes for tommorrow I'm feeling very jealous ( turning green )cannot get fishing til 15 January.