The pInvoke limitation is worse than you think... Your code may not require pInvoke, but MonoGame does ( that's how it calls to OpenGL ). I may be wrong, but im 90% certain the "free" version doesn't work with MonoGame.
Well MonoGame uses OpenTK for the OpenGL/ES backends. I checked the source code and it uses System.Runtime.InteropServices not DllImport or any of the other P/Invoke methods (although I don't know what InteropServices does in the backend).
EDIT: Information in this post is completely wrong and invalid.