Apparantly we have at work a hackerspace with 3D printer and the likes so I took the opportunity and printed the lens.stl focus tool posted here (thanks!). It works as advertised and I could focus for a distance of 2-3 inches. More than enough to inspect PCBs.
When I re-focus it to the 'normal' operation (e.g. factory setting), what object distance should I use? I would think that shorter than infinity will provide better range.

The tool inserted into the camera.

The tool upside down on top the the camera. You can see the portion that engaged the lens holder.

A close up of the tip. When tried to upload the stl file to an online 3D service I got an error message. As you can see there are gaps and irregularities in the printed part. Am not sure why. Might be a discontinuity in the 3D model.