How to replace the metaclasses of all the classes imported

[Jane Austine]

I know of import_with_metaclass at 
http://gnosis.cx/download/gnosis/magic/__init__.py but it doesn't help
in my case.

Say, I have a module A which imports module B with an ordinary
"import" statement. With import_with_metaclass I can replace the
metaclasses of all the classes in module A, but not those from module
B.

What I'd like to do is substitute the whole metaclass of the system
without touching all the codes.

Jane