C# CSharpCodeProvider: executing method in "compiling assembly" without adding reference

I am using CSharpCodeProvider to compile C# into a dynamic assembly which contains methods that are called by an external software.

Let's take the following code string that I am compiling dynamically:

public static class Foo 
{
    public static object Bar(a, b) {
         return NameSpace.Type.Method(a, b); // Need to call original/compiling assembly
    }
}

What I really want to do when calling NameSpace.Type.Method, is to call a method inside the assembly that originally compiled the C# code (i.e. the one using the CSharpCodeProvider).

That said, I cannot use ReferencedAssemblies.Add to pass it into the CSharpCodeProvider. This is because my assembly (DLL) is wrapped in such a way that it is dynamically loaded - i.e. it exists nowhere on the file system.

Is there any other way to call a method on the compiling assembly?