When creating a systemd container, what would be the best way to execute properties before propellor is run inside the container proper?

I'm trying to setup packages for networking in a systemd container, but I first need the network to get the packages. Ideally, we should be able to run a few properties on the chroot that are used when creating a systemd container (and therefore use the host network). So far, I've solved this by adding the properties in the Systemd.Core.installed property. Not nice, but works if all your systemd containers are the same. I've tried creating a chroot myself, tar it and pass that to Systemd.container, but things got a little complicated. It also requires additional properties on the host that have to be moved if the container moved to another host.