SD Wan - How to Exclude Traffic form one Interface for a specific WAN

Hello,

i have 3 WANs configured properly with SD WAN and Load Balancing with Spillover. I also have some Policy Routes to route specific traffic via a specific Interface.

What i'm unsure about is if it is possible to create a rule to prevent traffic from a defined source/interface to use a specific WAN connection, e.g. all Traffic from guests may not use WAN3 as this is the last backup and therefore should only be available to important traffic...

Do you have any ideas? Thanks, Tobias