Start->Run Dialog - "Run as Administrator" checkbox?

I'm trying to find if there's a registry key to enable the "Run as Administrator" checkbox on the Start->Run Dialog in Windows 7 (similar to the "Run in Seperate Memory Space" checkbox which can be enabled in the registry). At a couple of sites I remember I had this option, however on my current PC it's not enabled/visible.

If you know of a way to enable this checkbox via registry, or if it's available by a 3rd-party toolkit, please point me in the right direction?

I already know how to create a shortcut and set "Run as Administrator" on a specific application, and the "runas" command, I'm looking to enable the checkbox in the Start->Run command specifically in this instance.

Thanks.