Reserve a DHCP for a WAN backup

I have added a backup WAN line set to Failover. All is working well.

The backup line is a Verizon ASK-NCM1100 %G/LTE router set to Bridge/IPPassthrough. If the Verizon box reboots, it provides an a different DHCP/IP address, and I cannot connect to it. The only way I can find to access the DHCP settings if via the Network Manager dialog, where there are DHCP, PPoE, and Static options. I have DHCP selected but was hoping to find a way to reserve an address. Is this possible?