1. Edit the workflow definition:
2. Add an item type attribute. Let's call it MsgFromRrole of type ROLE
3. Add a message attribute called #FROM_ROLE of type ROLE with its value being the item attribute MsgFromRole.
4. In your plsql code (for instance when you instanciate the workflow process) set the value of MsgFromRole to 'SYSADMIN'. Use WF_ENGINE.SetItemAttrText for this.