Azure Express Route and VPN tunnel priorities

Hello, A customer has an existing VPN tunnel to the Azure vnet, and also wants to connect Express Route circuit to the same vnet. The issue is, that for some time, VPN connection must be preferred over the Express Route connectivity, until customer decides to roll over to new circuit.
Can you please tell, is it possible to maintain the VPN tunnel priority without advertising the more specific routes through the tunnel? E.g., if we do as-path-prepend on the routes for ExR (and modify local preference on the local devices), will it be enough to prioritize a route through VPN tunnel on Azure side? Or, none will work and we will have to advertise more specific routes in advance to ensure traffic won't fall over.

Thank you