How to get MaaS Regional controller IP/FQDN in preseed files via {{var}}?

Hello
Is it possible to get REGION controller IP/FQDN via variables in preseed files?
I am able to get RACK controller used for booting during deployment {{node.boot_cluster_ip}} but unable to find the way how to get region one directly from preseed file (maas cli can’t be used).
Is it possible? Thank you!