I know I'm a little bit late on this but I did say the weekend I'd get to it.
But here is the non destructive way of modifying it. It took less than 15 minutes.
First your Fujinon 55 1.8 maybe different as the non-EBC and EBC versions are built differently shell wise but mine was held together by three screws. My EBC 55 is solid and glued together so taking those apart will be much harder. Once the three screws are off you should get the following
http://dwo.net23.net/forum/gallery/image.php?album_id=5&image_id=125
The two columns on the right hand side are the control mechanism for the aperture. The left column is the aperture size itself and the right one controls the opening and closing.
So in order to make it manual, I wedged a piece of a cut hollow cotton swab tip (in pink) to between the pin and the base of the pin. As shown in the picture
http://dwo.net23.net/forum/gallery/image.php?album_id=5&image_id=123 http://dwo.net23.net/forum/gallery/image.php?album_id=5&image_id=124
I believe that most of the M42 pin designs are similar to this. I know the ones that I have taken apart are pretty much the same with very little variation. Here is the key though. The wedge you place in between the pin and the base of the pin should be long enough to hold it down at the maximum depth as the Fujinon aperture design requires the button to be pressed fully to get the aperture closed down fully. Otherwise you end up with aperture not fully stopping down which is my case right now. Anything past f8 has the blades staying at f8 size, which is easily rectified by adjusting the length of the wedge.
As for glue and acetone. I'd be really careful about that as acetone if spilled may affect the grease for the focusing mechanism and the black paint.
Edit:
Oh and for placing it all back together you have to be careful as now that you wedged the pin down the mechanism that controls the opening and closing column is at the original location but the control arm is slightly skewed. In order to place it in the right location just use the precision screwdriver to hold the control arm in the proper location and gentle lower the bottom piece once you get it in the right location remove the screwdriver careful not the hit the rear element and then screw the three bolts back in and your in business.