Never tried it but have you tried adding a custom option of 003 (default gateway)?
Believe my colleague got this working on a Meraki stack where we needed such a setup
Darren OConnor | doconnor@resalire.co.uk
https://www.linkedin.com/in/darrenoconnor/
I'm not an employee of Cisco/Meraki. My posts are based on Meraki best practice and what has worked for me in the field.