I am trying to pass a Business Object as a parameter to a routine, and adjust details on the calling Buisness Object

So a simplified version of my code is:    

  

The compliler is objecting that myBO is readonly.

Is there a way to amend the Calling Business Object in the Called Method. If I take out the Call By reference, just the copy that is called gets updated, but I want it to percolate back to the Calling Business Object