Using Service Broker internal to a single SQL Express instance?
From what I understand the limitation only applies when you attempt to send messages outside of the instance. Sending messages within the same instance is not limited by using Express. See the last reply in the following link:

http://social.msdn.microsoft.com/Forums/en-US/sqlservicebroker/thread/3b03a610-8159-4be8-b2d8-e2abb4ba1225

I hope this helps you.