I have used this 18 ~ 55 mm lens on M43 in unmodified form by holding the aperture lever at about f/8 with heatshrink tubing slid over the lever. This does not hurt the lens.
On a Pentax film slr, the lens vignettes slightly below 20mm or so.
Here is a link to a disassembly procedure. I have not tried, but if you are handy, it might be possible to lock the aperture ring at about f/8 for example by replacing the spring with a solid wire. For the camera metering to work, you would also have to fix the aperture position lever at the same level as the aperture is locked at. Tricky, but it might be possible with some research and fiddling,