How to check whats in a substitute's inbox?

Hello Workflow Gurus,

We are upgrading from 4.6C to ECC6.0. We are in the process of our Iteration testing. I have a scenario where I need to put in a user as my substitute and to check if its working, I create a PO or a Purchase Req. The PO should be in my inbox as well as the substitute's inbox. To check if the PO is in my substitute's inbox, is there a transaction that I could use to see the substitute's inbox? I use SWI5 all the time to check work items in other user's inbox. But when I set up a substitute and look for WI's in his inbox, it never comes up with anything using SWI5.

Any help is truly appreciated

Thanks