How can I convert an existing Ember initializer to use the newer instanceInitializer format?

I am trying to figure out how to convert an existing initializer to the newer instanceInitializer/initializer format that is in Ember 1.11+ (http://ift.tt/1B0z5ED)

Here is my existing initializer:

app/initializers/session.coffee (ps this is to stick the logged in user onto the client session using ember-simple-auth)

import Ember from 'ember'
import Session from 'simple-auth/session'


UserSession = Session.extend
  # Here we set the 'session.context' property which is used for 
  # filtering the User contexts throughout the site.
  context: (->
    user = @get 'user'

    # Check for a defaultContext and use that otherwise use empty.
    if user and user.defaultContext
      @container.lookup('store:main')
                .find('context', user.defaultContext)
                .then (context)=>
        @set 'context', context
    else
      @container.lookup('store:main').createRecord 'context'
  ).property 'user'

# Takes two parameters: container and app
initialize = (container, app) ->
  container.register 'session:usersession', UserSession

UserSessionInitializer =
  name: 'session'
  before: 'simple-auth'
  initialize: initialize

export default UserSessionInitializer

So I tried to split out the UserSession stuff which contains the @container.lookup into app/instance-initializers/session.coffee but then I need to import it in the initializer/session.coffee because the container.register uses UserSession

Any help on how this should work is appreciated!

Thanks