Internally I'd expect you to have to add every subdomain to the DNS entry page. This populates the /etc/hosts file which does not support wildcard entries. There may, however, be an alternative. In /etc/dnsmasq.conf or better still, in a file of your own in /etc/dnsmasq.d/ make an entry:Obviously change xxxxx.lan to your LAN domain and the IP address to the ClearOS LAN address. Once you've made the change, restart dnsmasq with a "service dnsmasq restart".
Having said this, I don't know how this then leaves your other entries in the hosts file. I don't know if the hosts file entries are used or if you always get your ClearOS LAN IP returned. You'll have to test that