I first got into Fimo to make 'modelling lights' for a pair of Vivitar 283's. I used standard screw shells to power some 50W mini spot light bulbs. I used the Fimo to make a pair of U shaped affairs to hold the screw shell sockets on top of the flashes. I held this affair together with some velcro, and the occasional rubber band.
The next use was in the Metz 60CT1 pack and flash that came my way for $20. One side where the clip for the shoulder strap attaches was all banged up and about to come apart. I mashed Fimo into the void where the corner was suppose to be, and after drying, filed it to the desired shape, and wrapped a couple of turns of self amallgamating tape around it. It has held that way for the last 4 years.
I have a shade that I use as a compendium style shade for my Cambo monorail. I fashioned a ring that slips over the front of the usual lens, a single coated Symmar S, to help give it more contrast. I don't have the right sized adapter ring, so I made one out of Fimo, and coated it with slow setting hot melt glue on the sides to strengthen it.
I have also used a donut of it molded to fit against a 35mm camera for which I did not have a reversing ring or extension tube for, to do some macro work before I came across a bellows rig for it.
I made a stiff paper tube to fit the mount size, and taped the tube to fit flush to the lens mount. I then applied the soft Fimo donut, and pressed it around the tube and against the slr body to get a good fit. I moulded flat ridges against the body side of it to allow C clamps to hold it to the camera, and cast small hardwood blocks to fit there to distribute the clamp force better than the plaster on its own would. Once it had dried I removed the tube, sanded it to clean it up a bit, and then sprayed the inside and out flat black. The lens front was wrapped with teflon tape, and set centred on the sanded flat front of this affair. Hot glue was applied and pressed into place. The teflon was pulled clear once the glue dried. The lens was attached to this thing using a small tensor bandage. It was not pretty, but those were my uni student days, when finds were tighter than free time to fiddle with this sort of thing.
Hope these examples get your creative juices flowing towards a solution.