According to "Jens" the plastic wheel can be removed by turnig it counter-clockwise when the gear is blocked. "Julien" found a YouTube-Video showing how to proceed. Starting at 7:25. Thank you to Jens and Julien.

No need to proceed with the custom tool if the plastic wheel has already been removed in the previous step

The tricky part is to unscrew the Tx20 screw located under the plastic wheel

I was not able to pull the plastic wheel from the shaft

If you like the risk you might drill a hole in the plastic wheel for easy access

I used a custom tool -> see next step