Canaries and wildcard sourceLabel routing


I have two environments, dev and qa, that use sourceLabel routing to keep separate. There are subsets for each, and a routing rule that checks the sourceLabel and routes to the appropriate subset. This all works great.

I would like to deploy a set of canaries for the dev environment, say subsets dev-canary1 and dev-canary2. I would like to set up a rule such that the dev1-canary will call other services using the dev1-canary subset if it exists, but if it does not, fall back to the regular dev subset for that destination. I would like to do this without deploying the destination services each time a canary goes out.

As all labels do start with dev, I tried using sourceLabels: dev-* but sadly it seems that wildcards are not supported here.

Any suggestions on how to create this fallback routing rule?