In October, the SQL Server 2008 Feature Pack became available and included in it a new External Activator for Service Broker. Documentation is lack luster in the Books Online, but documentation actually comes with the installation that you would probably never find unless you knew about it. Thanks to The Bit Bucket (Greg Low) from SQL Down Under who pointed out that documentation ships with the External Activator in the C:\Program Files\Service Broker folder. You can find a Word document called SSBEA.docx in this path that has the documentation.
To download the Feature Pack see: