Hi Eric,
You should be able to achieve it by using protocol binding settings:
Dual WAN--> click on WAN (1 or 2) icon --> scroll down to protocol binding --> add specific rule for all services where source IP address would be your particular LAN host IP (repeated twice if it is only 1 host) and destination 0.0.0.0 (repeated twice) choose desire WAN1 or WAN2.
I hope this helps,
Aleksandra