Invoice approval workflow for Admins that support more than one department

Content

Our current invoice approval workflow is setup utilizing our management hierarchy structure from our HR system.  (i.e. the direct supervisor of the requestor provides the approval).  However, we have some instances where although an associate has one manager, they may support multiple areas and therefore the approval should go to someone other than the direct supervisor. 

Does anyone have a similar issue and if so, how did you solve for this without specific workflow coding for user names?

Version

R13 20D