I get this error when i use "workflow" in the .js file org.mozilla.javascript.EcmaError - ReferenceError: "workflow" is not defined. (AlfrescoScript#3)
but the reference to same object from the template file works fine.
Looks like you can't. I just checked, and with 2.2 you can't either. It does make sense it's exposed in some of the newer stuff, since with adding multi-tenancy, they are exposing workflow to be easily dynamically reloaded.
You can look inside script-services-context.xml to see how these things get exposed, and follow the code. It might be not too hard, actually, depending of course on how much functionality you need exposed.
If you need an example, I can email you a sample I put together for how to expose this - not relating to workflow, but might help (it will be part of our upcoming enterprise network). Email me at jbarmash at alfresco dot com.