Ah, es kommt Licht ins Dunkel ...
Felix, take a der cable and smash the end flat and insert in from the bottom of the delrin housing stop. This cable will attach to the der with the der moved to the large chainring and the delrin stop about 1/2” from the frame mounting bolt on the ST as shown in the picture. This is not critical but the closer it is to the ST cable mounting bolt the better but not closer than 1/2”. Cut housing to length so that it is ALMOST straight between frame stop on DT to the delrin stop. Insert der cable from shifter through the housing and into the top of the delrin and force the housing into the delrin and attach that cable to the frame bolt on the ST with shifter in large chainring position. You want to end up with some slack or bend in the housing but not much when in the large chainring. When you shift to small ring this housing will bend more. As you shift to large ring the housing will push down on the delrin and thusly pull down on the der arm.
I know this is hard to grasp as it is not the norm but it works really well once you understand how it works. A couple of companies licensed this housing push method from me for their brakes. I don’t know how well it worked for that but the housing can more than handle the compression of the derailleur.
I think the action works best if you use the coiled type of housing instead of the SIS straight wire housing for at least this short piece of housing. SIS from shifter to frame stop is best. Also later models used a ferrule in the delrin. I can’t remember if I made the delrin hole large enough for a ferrule or not, I think I did.
