pass arg to workflow

I am  using a Workflow and within this workflow I want to send a MSG.EXE to remote machines.   I have tried to place a Read-Host command within the Workflow Loop and it gives me an error saying you can't do that.  So I moved my Read-Host Outside the  Workflow Loop and it still does not work.  No MSG ever gets sent to my remote machines.  

how can I pass an $arg into a Workflow Loop?  

mqh7