Hallo Markus,
no, for now I got along with a workaround. After my quick&dirty-solution someone answered with a hint:
Please have a look at the discussion on https://moodle.org/mod/forum/discuss.php?d=105653. There's a possible solution there (by Brian Pool).
I guess I already saw this post as I found the file autouploaduser.php in my download folder but I haven't given it a try yet. because meanwhile I had prepared a tool that simulates the mouse clicks in a browser to import the nightly file as an admin user and for now it is working while I care for other urgent issues .
Let's keep in touch if you try the solution by Brian Pool.
But if you like to try my workaround for Chrome, you can find a zip attached with the source, the exe and the batch to launch it.
Alles Gute,,
Michael
P.S. Ich habe auf Englisch geschrieben, weil wir hier in der englischen comunity sind.