Enabling Image Resizing not per-domain

I need to use Image Resizing ONLY via worker (i.e. no /cdn-cgi/image path), but the worker will be deployed on about 20 different domains. I will not buy 20 pro licenses to do this, but it seems like Image Resizing via worker is tied to the cdn-cgi/image version for some reason.

How can I enable Image Resizing for my worker without enabling it for each domain?