Here is a way to add an as_dict() method on every class, as well as any other method you want to have on every single class. Not sure if this is the desired way or not, but it works...
class Base(object):
def as_dict(self):
return dict((c.name,
getattr(self, c.name))
for c in self.__table__.columns)
Base = declarative_base(cls=Base)