def mysurface(object):
    def __init__(self, surface):
        self._surface = surface

    def blit(self, source, dest, area=None, special_flags = 0):
        return self._surface.blit(source, dest, area, special_flags)

    # code to forward all the other members

    def myblit(self, source, dest):
        # code that modifies source and dest
        return self._surface.blit(source, dest)

 mysurf = mysurface(pygame.display.set_mode())