Unattended Install - Single Installer, Multiple Configs

After reading the documentation for bsdinstall about unattended
installation, I have a question about alternatives. I have a goal of having
a set of different configurations that will be installed automatically. It
appears that this would require creating separate media (ISO images) for
each variation. Is there an alternative where the installation media can be
modified in a generic way which would then have bsdinstall search
for installerconfig in a separate location like another mounted ISO? The
reason for this would be to make the modification to the installer once and
then have the variants held in smaller, faster to create ISOs. This is the
paradigm for Windows where the installer ISO will search for
autounattend.xml in the root of a mounted CD image. In a similar paradigm,
Ubuntu's installer ISO requires that the grub.cfg file be modified to add
"autoinstall" and then the ISO rebuilt. The installer then searches for
user-data and meta-data on a mounted CD with an image name CIDATA. Both of
these paradigms have a single large installer ISO and as many smaller
config-only ISOs for each different variation to be deployed.

Is there a way to do something similar with FreeBSD bsdinstall, or
is the only option to make a full ISO for each variation?