Send server-down when all pool members down

I've been trying to write rules to send a page to the client when all nodes are down.

 

I'm using "HTTP:respond 503 content ...", but can't do this in the HTTP_REQUEST event because it hasn't tried to select the node yet, and can't put it in LB_FAILED, presumably because the HTTP:: namespace doesn't exist within that event (or something like that).

 

 

Can anyone set me straight?