Unless there is a requirement to to use Windows authentication I would rather recommend certificate authentication between the servers.

I wrote a tutorial with examples (for personal use) a few years ago that has a step by step description on how to set up service broker between two instances that uses certificates for transport and dialog security. The only requirement if you use certificates is that the two servers can communicate over a port that you select when you create the service broker endpoints.

I can find it tomorrow when I'm at work a post it here if you want to.