how to share a bean across modules in spring xd

Lets say I want to create a stream with this defintion

file | serviceActivator1 | transform | serviceActivator2

So I have two custom modules in this definition. My understanding is that spring xd will create a child context of each component/module and deploy it in a container.

How can I share a single bean across serviceActivator1 and serviceActivator2. Basically this bean should be defined in the parent context, not the child context of each module.