I think the problem with doing a blind import of the parent package is it would be hard to differentiate between the ImportError when the package (or an ancestor) is missing, versus a user-generated ImportError. Maybe you could inspect the exception as a workaround (untested):

try:
    __import__(pkg_name)
except ImportError as err:
    if err.name != pkg_name and not pkg_name.startswith(err.name + "."):
        raise
    raise error(format(err))