Im going to play the pure Meraki card here
Option 1 - vMX in Azure will do your AutoVPN to all participating networks
Option 2 - Beta Firmware (15.xx) and Azure VPN Gateway - I have done this, it is simple enough, but ive found that the tunnels were either a) really stable or b) really not.
The vMX is not much more expensive than a standard VPN Gateway, and if you couple a Reserved Instance with the vMX, it is very compelling
The other alternative is AZURE VIRTUAL WAN!! And if you do get that working, please let us know your experience.
I have to say, Philip's method is one im going to investigate however!