Dtab alternate not chosen over higher-precedence failing service

Expected behavior

Suppose I have a dtab

  /svc => /$/namer/srv1 | /$/namer/srv2

I would expect that if every request issued to srv1 resulted in a failure, requests would start being sent to srv2 instead.

Actual behavior

So long as srv1 can be bound to an address, it receives all the traffic.

Is there any way to make it so that srv1 failures will result in requests being routed to srv2? I want srv1 to get traffic preferentially, and I don't want to rely solely on a namer's active health checks to control that.