How do I allow a group to manage a systemd service using polkit?

I have a service (some-service) on my system that I'd like to allow members of group managers to control (start, stop, restart). I would also allow these users to use PolicyKit instead of sudo for various reasons.

However, Ubuntu 16.04 does not (yet) have PolicyKit version 0.106, meaning the rules system present in that version does not exist, meaning I need to use PKLA files as documented here.

How would I write these rules on PolicyKit 0.105 and only allow managers to only control some-service?