There is another option but you would need a third device.
In this case, it would be configuring a VPN with another device on the MX network side (such as a router, Linux, Mikrotik, etc.). Create a link between it and the MX or use an existing network, and create a route pointing this device as the next hop to the desired networks on the other side, so you can enable Auto VPN.
It's not the best solution but it works.
I am not a Cisco Meraki employee. My suggestions are based on documentation of Meraki best practices and day-to-day experience.
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