> It is possible to generate interface definitions in C# on the fly (at run-time),

Huh, I never thought about this restriction, so you can't add a new interface with 'Reflection.Emit', you can only add a class that implements an existing Interface, is that right?

> but unfortunately it requires going outside of the CLR or even the DLR.

By this do you mean writing raw CLR metadata yourself and then somehow injecting it into the running process or something else? Either way, its sounds like an interesting technique, any links to how it's done?