4" PVC or ABS pipe cap, then line inside with weather stripping/felt, etc to get snug fit (95mm = 3.74" ) . I did it with a Mamiya 645 200/2.8 APO that I wanted to cap with the hood in place. Works wonders. They have a lighter/thinner blue cap, a temp one IIRC for 4" ABS that works well.
Also Profoto lamp bodies are 4" outside diameter. Could possibly due same with a flat D1 monolight cap.
I've done the coffee can lid thing with a Nikon 200/2 VR and it works, but something harder like PVC or ABS, etc is far more puncture proof and more consistent with a 'normal' lens cap.