Modify header to disallow compression per docker service

I'm running a docker instance of OpenSpeedtest behind traefik.
The reported upload rates are unrealistically high (over 2000 Mbps on a line with 30 Mbps upload, see Unrealisticly high upload measurements · Issue #4 · openspeedtest/Speed-Test · GitHub).

My guess is, that the generated upload data is compressed by the browser. This would make it seem like much more data has been sent than it was actually transmitted over the line.

This issue does not seem to occur when the container is directly used with it's nginx based web server.

Is there a way to configure a header for this specific docker service with a label that tells the client to not compress post data?