Run an update *one* time at shutdown – systemd-run?

I've got a few things that I don't want to update while my graphical session is running, but would be happy to have them updated on shutdown (after my graphical session ended, while network is still up), *once*. So, I don't want to write a service file, enable it, and then have it run at *every* shutdown. Now, I thought, OK, systemd-run to the rescue:

systemd-run \
           --property=Type=oneshot \
           --property=DefaultDependencies=no \
           --property=Requires=network.service \
           --property=WantedBy=shutdown.target \
           /usr/bin/dnf5 update -y package1 packge2…

But that fails with

Failed to start transient service unit: Dependency type WantedBy may not be created transiently.

Is there another way to this?