Substitute User workflow permissions

Hello,

Not sure if we don't have something setup correctly but we have a pretty extensive workflow with NACL permissions on the document depending on who the document is assigned to and who can approve it.  We also have permissions for the workflow state transition on who can move the workflow to the next workflow state.  When using Substitute Users we have noticed that the Substitute can't move the document to the next when we put the Assigned to permission in the State Transition tab.  Unfortunately there is no built-in Substitute user property either.  

Is there a better way about doing this?

Thanks

Jeff W.