WCF 4.0 Routing Service for Publisher/Subscribers implementation

Question

My attached simple case of the Pub/Sub implementation using Routing Service is very ideal and it is able to achieve this:

Publisher sent messages via Routing Service, and all those Subscribers are able to receive the same messages from the Publisher. However, the condition is that those Subscribers must come "alive" before the Publisher sent the message. If the Publisher sent messages before the Subscribers come "alive", those messages would not be received by the Subscribers when they come alive.
 
I would like to modify it such that even those Subscribers come "alive" after the Publisher sent the messages, those messages would still be able to be received by the Subscribers.
 
Which portion do I need to modify to cater to the above?