Get a Func<> from MethodInfo with private (inaccessible) types

Consider the following code:

private class ThirdPartyClass {
    private class InternalPrivateClass { }
    private static int SomeFunc(InternalPrivateClass t1) { 
        return 0; 
    }
}

I have no control over ThirdPartyClass. I want to be able to quickly call SomeFunc without the performance overheads of reflection. So what I have so far:

Type t = typeof(ThirdPartyClass);
MethodInfo mi = t.GetMethod("SomeFunc", BindingFlags.NonPublic | BindingFlags.Static);
// ...now what?

• Calling mi.Invoke() is of course slow, because it's using reflection.
• Delegate.CreateDelegate(typeof(Func<object, int>), mi); fails because the Func signature must match exactly and (object, int) doesn't match the MethodInfo's signature (ThirdPartyClass.InternalPrivateClass, int)
• Constructing a properly typed Delegate via reflection (see https://stackoverflow.com/a/40579063/2692950) only lets me call .DynamicInvoke() which is still slow. I cannot cast this delegate to a Func to be able to invoke it directly because, again, the signatures don't match.
• I cannot write Func<ThirdPartyClass.InternalPrivateClass, int> - it won't compile since InternalPrivateClass is private.

ᅟ

Why I need this:

Take a look at this MD4 hash implementation: https://stackoverflow.com/a/46821287/2692950

This works very well, except that every single hashing operation is calling a method via reflection!

(If anyone knows of a better way to implement obtaining a crypto service provider directly by ALG_ID, I'm all ears :)