> own metaclass. (David ?)

Simply use the __class__ attribute of a Boost.Python wrapped class.
I.e. if the class is "bar" (and you construct objects with "bar()"), bar.__class__
will give you the metaclass.
See also: boost/libs/python/doc/tutorial/doc/tutorial.qbk
Look for:  __metaclass__

But, like Hans I'm also a bit skeptical ...
Ralf