Using Run with Arguments shell extension with "as Admin"

I have used various versions of Kel's UberPack for several years.  One of its features I have enjoyed most is "Run with Arguments" in the context menu.

There are several registry entries for RunARG. One example is:

Windows Registry Editor Version 5.00[HKEY_CLASSES_ROOT\batfile\shell\Run With Arguments][HKEY_CLASSES_ROOT\batfile\shell\Run With Arguments\command]@="\"C:\\Windows\\system32\\RunArg.exe\" %1" 

What I'd like to do is create a shell extension to "Run with Arguments (as Admin or Elevated)"

I found the following command-line.

runas /user:REQUIREDUSERNAME /savecred C:\Windows\System32\RunARG.exe

I guess /savecred is supposed to make it ask for admin password on the first run only.

1. Does anyone know how this might be used to edit the context menu item so it can be run with elevated privileges?
2. Does anyone know if that command-line will work using the %USERNAME% variable?

I considered checking the Run as Administrator box in the executable's Compatibility properties, but then I'd be nagged by UAC every time I use RunARG.  Using runas with /savecred would be most unobtrusive, if it can be made to work in the context menu. 

(I don't currently have any virtual machines to try this out on, so I just figured I'd put the question to the group.)