Have a 3011 with a single Public WAN address via a /30 provided by Fiber provider Southern Light.

Hosted VOIP supplier "CSPIRE" must have a dedicated connection with public IP so we have a new address assigned ( /30) which I have added to the WAN
facing interface and it can now be pinged from outside networks.
What are methods for a single Internal subnet "10.10.76.0/24" to only transverse the new "secondary" public IP while leaving all other traffic routes over the primary WAN IP.
Or course Dst Address = 0.0.0.0 for the primary route gateway primary WAN IP. Ethernet 1 is currently scrnat masqueraded . Are separate masq rules desired?

Is there a route table notation for all addresses excluding subnets ? ie 0.0.0.0 except 10.10.76.0/24 ?