Hi Richard,
It could work.
You can whitelist (http://help.hotspotsystem.com/knowledgebase/using-mac-authentication-macauth) the MAC address in the Rocket M2 in /etc/chilli/defaults for any device (C7 here) that has a NAT firewall (regular router mode). In this case it hides all devices behind and seems (from WAN) on its NAT only, and since you whitelist its MAC all devices get free internet from behind.
Best,
Steve Hars