For the front rings, I go to a hardware store and find a piece of pvc pipe fitting in the plumbing section, or improvise a similar correct-diameter hollow tube. Then I tear thin strips of duct tape to make a cushion on the edge of the pipe fitting. This cushion gives friction so I can push down on that lens ring to try to get a "grab" so I can start turning. Sometimes it works, sometimes it doesn't. Usually does eventually though. As for the super-tiny set screws, if you use a 50m lens turned-around-backwards, you will see that many of them actually have a very wide slot, and the cheapo screwdrivers may NOT be wide enough, and the slot therefore gets torn up beyond hope if you're not careful. I'm convinced if you send a lens off to Hassselblad or somesuch firm, they just throw away the screws and use new ones when they put your item back together. We don't have that luxury.
Look for sink stoppers, sometimes you can find them just the right size.