Simply put, it's not possible. You just can't stop an application using the .NET framework if you're letting it compile into that. You can, however, (programatically) disassemble the code, analysing all calls, seeing if its to the .NET framework and not allowing the application to run or similar action. Alternatively, you could possibly patch the target method and make it throw an exception. I haven't that much experience with detouring .NET applications though, so I'm not sure of the implications this would have (are the libraries shared in the same app domain, module or process etc).
It'd be easier to use Javascript or something. Syntax is similar. Libraries and wqhitelisted methods can be exposed and so on.