Workflow Substitution

[Smith, Cassaundra]

Does anybody know how to restrict what workflow workitems a substitute can see??
I was reading in SAP help where you could restrict on a profile field available
when you setup a substitute.  Does anybody know what his profile is??  There is
a drop down on this field  with only three choices. Can you somehow set this
profile on a workitem you want the substitute to see??
 
We are on SAP 4.6C.
 
Casey