[Spinnaker]

Been following your progress with interest. I have always prided myself with having good problem solving skills and this one keeps me engaged. Not having in person first hand knowledge of the problem site makes it even more of a challenge.
First, I would like to know if you can rotate the chain and sprocket?
If that is possible, this is what I had in mind.
Get some of those small rare earth magnets and stick them on the chain in between the sprocket teeth. Rotate the chain and sprocket to where the set screw is and see if they can attract it and stick to the magnets. If they do, you can rotate the chain back and grab the set screw. Not much chance of losing the magnets, as they stick like crazy to anything ferrous. Just make sure to count how many magnets you use and account for them afterwards. The ones in the picture are from Harbor 'Fright'.

edit:
* Opps, I see that you have already thought of this upon reading earlier posts.*