I hear you. Unfortunately there will not be an easy way to that, currently. To get a whole subnet to use a different outbound IP you will only be able to do that if the IP belongs to the WAN interface and as someone mentioned above you could achieve that with another L3 device connected to WAN2. ... View more

The only way to achieve that would be to configure a 1:1 NAT under Security Appliance>Firewall. All inbound and outbound traffic would then be NAT'd to the new IP instead of the MX's.    Have a look here for more info on how to do it:   https://documentation.meraki.com/MX-Z/NAT_and_Port_Forwarding/Port_Forwarding_and_NAT_Rules_on_the_MX ... View more