The above version worked surprisingly well, but it was ugly, so I decided to remake the cams, rods, and what the hell, the drive shaft too. Cams and rods are made with carbon fibre (this stuff is amazing...), the rods with larger 10 mm flanged bearings, and the drive shaft uses some decent u-joints, 8mm alumium rods and 12 mm aluminium tubes. They're held together and are adjustable in length using aluminium shaft couplers with 8 mm openings at one end and 12 mm at the other. Works great.
All in all very happy with the mod. The pedals are really silent, smooth and look pretty good. The total cost of the materials for the mod came out at about €40.