Workflow with two receive activities and correlation

I've a workflow that has two receive activities in a pick activity. Whenever I get a reque开发者_运维技巧st in the first request activity the workflow has to create a new instance while if the second receive activity get requests it should not create a new instance instead the messages should be routed to the already running instance (there should be an instance running already). How can I handle this?

I did some blog posts about how to setup message correlation to do this. Check here for a good starting point.