No sorry you dont have to go Landing page then. You would need to activate switch
HCM_MSS_WDA_2 then to get substitution functionality without landing page, if you see from landing page we call WDA abap page for substitution. read here as it has all the info you need. http://help.sap.com/erp_hcm_ias_2013_02/helpdata/en/37/878a840ff940b6b12382485e720bd7/content.htmhttp://scn.sap.com/community/erp/hcm/employee-self-service/blog/2013/02/07/all-that-is-needed-for-configuring-substitution-in-mss hope this helps to clarify