Hmmm... why?
I doubt it's worthwhile for the code generator to detect what is and isn't
being used by the code it's generating.
What I suggest is to go into Project|Add reference and grab all the
components you think you might ever use.
If you're generating code do you really need a project file? It seems to me
that only Visual Studio needs project files. Do you really need to edit your
generated code in VS?
I don't currently do any code generation, but I do write a lot of code (for
libraries) outside of VS and then use a make file to create my libraries.
Of course that still means I need to list the namespaces in the make file,
but that's a manual process anyway. Listing unused namespaces won't hurt or
bloat your code so you can add all you like.