External image as community icon/banner?

I'm trying to setup a community without pict-rs (and as such, without being able to host its pictures myself). I've been tinkering a bit with the API (through python clients, essentially), and I've found how to change my users's avatar to an URL, but not a community. On Lemmy.py, for instance, I have an update() method a community object, but it can't seem to modify anything...

Has anyone an idea? Thx