Done!
I have a ToUcam adapter with the buffered bore - which is just a threaded surface. I cut a coiled spring to give me two "C" clips that were just larger than the bore. I carefully inserted one end of the "C" and then compressed the clip in to place with the butt of a drill bit which just fit the bore. I got it down about 6mm, cleaned and placed the filter in and then repeated for the top clip.
Sorry about the fuzzy photo