Hi there,
we just forgot about the topic, because it did not work at the time and it wasnt that important but wouldve been a nice feature.
I just got some notifications, that this post is getting replies, and we have updated since a few minor versions.
The Problem seems to be fixed, alt least in : Checkmk Enterprise Edition 2.1.0p38
It works currently, so in the meantime there was probably a fix for the problem. 
headers={
‘Content-Type’ : ‘application/json’
},
json={
‘mode’ : ‘fix_all’,
},