.net - Is An Extension Method The Only Way To Add A Function To An Enum

I have a Direction Enum:

Public Enum Direction
Left
Right
Top
Bottom
End Enum

And Sometimes I need to get the inverse, so it seems nice to write:

SomeDirection.Inverse()

But I can't put a method on an enum! However, I can add an Extension Method (VS2008+) to it.

In VB, Extension Methods must be inside Modules. I really don't like modules that much, and I'm trying to write a (moderately) simple class that I can share in a single file to be plugged into other projects.

Modules can only reside in the file/namespace level so I have one in the bottom of the file now:

Public Class MyClass
'...'
End Class

[Code]....

It works, and "if it ain't broke, don't fix it", but I'd love to know if I'm doing it wrong and there's a better way with less boilerplate. Maybe in .NET 4?

Finally, I know I could write a structure that behaves like an enum, but that seems even more backwards.