As a workaround for this missing feature,
the negative number matching regexp can be used for allowing arguments starting with '-' in arguments of option flags.

We basically do:
parser = argparse.ArgumentParser(...)
parser._negative_number_matcher = re.compile(r'^-.+$')

This allow cases such as @andersk:
$ a2x --asciidoc-opts --safe gitcli.txt
where '--safe' is an argument to '--asciidoc-opts'

As this behavioral change is quite simple, couldn't the requested feature be implemented like this with an optional setting to the ArgumentParser contructor?