C# - How To Protect Net Winforms Assembly From Customers Of A Customer

This question appears to have died, so I've decided to offer a bounty.What I'm most interested in knowing is if my scenario in the ETA1 below is viable and is used. If it isn't, then a good explanation of why not would be a good answer. Another good answer would be an alternative (but not including the internalsvisibleto attribute).

The best answer would be, yes, it's viable, everyone does it and customers love it!ETA2: I think I've thought of a good solution. I provide the customer with a distributable edition that is as functional as their edition but is unlicensed and has the classes and members hidden, using attributes.
I can do this with compiler directives, on every single important member, but I wondered if there was some global way to hide all members of a class?

A simplified scenario I have a class that extends a control in someway and I want to sell my class under two licenses;

(1) Standard - The customer gets x number of controls that use my class but can't instantiate the class (its internal).

(2) Developer - The same as Standard except they can create their own controls that use my class.

My problem is that when the developer customer comes to sell their controls, they can't help but expose my class to all their customers.

The only way around it, in my scrambled mind, would be for the developer to somehow integrate my assembly into theirs, and in that way I can keep the constructor internal. Or, use the internals visible to attribute.

ETA1: I'm thinking aloud here, but, I could have a list of permissable calling assembly names which the customer could add to. When they ship their product, their customers' assemblies would not be in the list and therefore they wouldn't be able to instantiate certain classes. (The list could obviously be hashed).