One point worth clarifying initially is that the secondary WAN would be referred to as WAN2. Primary as WAN1.
If you go to Security Appliance>Traffic Shaping there are two options. Flow Preference - Internet Traffic and Flow Preference - VPN Traffic. It sounds like you are just wanting to configure the VPN traffic preference so you'd setup something like this. Remember this is destination-based routing so you'd have to configure accordingly.
Adam R MS | CISSP, CISM, VCP, MCITP, CCNP, ITILv3, CMNO
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