Run OS as other user? testing account on SSO

We wish to disable Native Authentication once we go live on V8.  If Native authentication is enabled, all users must enter their username and then the authentication occurs.  In V7, that wasn't required.  

In V7,  we utilize several native accounts for testing - i.e. TestUser1, TestUser2 - that the admins can leverage when working with security.  They use their SSO account to launch one window of OS and login natively with the test user on another instance of OS, enabling them to make a change in their admin window, refresh, and test the change in their other instance.

With disabling Native Authentication, our IT department suggested we create Azure test accounts that can authenticate  like our normal user account through the shift/right click and "run as other user" function to login as that t-account.  However, this doesn't seem to work - nothing happens after clicking on the shortcut and entering the t-account credentials.  

Is it safe to assume this method doesn't work?  Aside from turning on Native Authentication, how could our admins login as another user so they are able to test?