Enhancement to using directive formatting

A coworker has an interesting way of formatting using directives that might be worth supporting. He puts system and library usings at the top (outside the namespace) and puts usings for libraries that we developed inside the namespace.
Where I would do this:
using System;
using System.Text;

using SomeCompany.SomeLibrary

using MyCompany.OurLibrary;
using MyCompany.OurOtherLibrary;

namespace MyCompany.MyCode
{
     public class Foo

He would do this:
using System;
using System.Collections.Generic;
using System.Text;

using SomeCompany.SomeLibrary

namespace MyCompany.MyCode
{
     using OurLibrary;
     using OurOtherLibrary;
     public class Foo

What do you think of this approach?  It makes the distinction between our code and external code very clear, and shortens the name of our included namespaces, but by splitting the usings between two locations it makes it more difficult to see the entire picture of dependencies. How hard would it be to support this? Dave