How do I change the 'Platform Target' on compiled assemblies without having access to the source?

For this particular instance, I have an compiled, .NET assembly as a DLL that is marked as `x86` and I need to change it to `AnyCPU`.

Why?:

* Trouble dealing with this issue:
<http://blogs.msdn.com/b/visualstudio/archive/2010/06/19/resgen-exe-error-an-attempt-was-made-to-load-a-program-with-an-incorrect-format.aspx>
* Trouble with third party providers leaving assemblies on `AnyCPU` when dependant on `x86` libs.
* Trouble with third party providers leaving assemblies on `x86` when platform independant.