@CoolToys Yeah I thought about trying the split IP address technique.
Trouble with that is, when a device connects and asks for an IP address assignment from the DHCP server, both routers would see only it's MAC address and both attempt to assign it an IP address from both ranges. There is no "steering" mechanisms.
This is not "bridge mode". That could be done with most routers but then the user supplied router, in bridge mode, has it's DHCP server disabled. Only the master router assigns IP addresses and contains the NAT storage. Using the Bell HH4K DHCP server is the problem. There is no backup/restore facility.
PPPoE was the real only way this could work, allowing the HH4K router to just act like a dumb modem, and Bell has disabled this function in their routers.
Bell will not allow and will not support another modem on their fibre lines. The Netgear went back for refund. I am considering a different ISP now.