I had the same requirements and after so many searches it was clear that Administrator Rights are required in any case.
I have solved this issue by creating a new Application pool with Custom Account as Identity.
Basically my server was having 2 users. one Administrator and other user_account with same administrator group. But still user_account was unable ...
Add the following in the section system.webServer.
In IIS Manager root of website:
* enable Anonymous Authentication
* enable Forms Authentication
* .NET Authorization Rules: Deny Anonymous Users; Allow All Users