I suspect it's unlikely, but you'll never know until you ask, but are there any attributes that would allow us to contribute to
the compiled output?

e.g.

// this class exists in a separate, compiled assembly for the compiler to load during compilation
class MyMethodCompiler : Attribute
{
  // This is called during compilation
  public override void GenerateMethod(MethodBuilder method)
  {
     // modify the IL that was generated from the compiler
  }
}

// some class in a user assembly
class MyClass
{

  [MyMethodCompiler]
  public void SomeMethod(...)
  {
    // User code in method
    ...
    ...
    ...
  }
}