How do I tell systemd-logind that the session is not idle, without using a desktop environment or session manager?

Sadly, the lack of answers may mean that there isn't one. Happy to be wrong, though!

For those who may be researching the same thing, I finally caved in and am using a session manager. Specifically, sddm. Everything seems to be working fine, now, and the session manager really isn't too bloated and pretty much stays out of the way.