Another vote for putting a plastic sleeve over the pin on these type of lenses, even if it means taking the back off.
I bought a cheap M42 Super Paragon 135mm last week with no 'auto - man' switch like found on Tak's and Helios amongst others, the pin was the only method of operating the aperture.
Being lazy and not really wanting to take the rear of the lens apart I thought I would be clever and rotate a pressed alloy top hat shaped trim plate on the back of the lens that had a cutout for the aperture pin. I thought that by rotating it one screw hole the thin plate would hold the pin down.
It did, but too bloody well! it pushed the pin too far in and dislodged a spring in the levers rendering the aperture useless.
So I had to take the back off, then spend a fun hour or so figuring out where the spring should fit, and more importantly, how the hell to get it back in without a major stripdown!
I got it back in and working, and then sleeved the pin with the old faithful bit of Qtip.
Do it right, and do it once.