Implementing New Native Data Type

Hi!
This is a quite advanced question.
Is it possible to implement a new native data type?
From what i know, the base class library (BLS) is made in C#, and the virtual machine where .NET runs is made in C++. I couldn't find any way to do it, mainly because of security protections in the framework, most methods are internal (which means only system dlls can access them).
Maybe recreating the base functions in a lower level language like C++, and wrapping them around a .NET class might do the job.

What are your ideas/opinions?

Thanks in advance,
JCC