in dh_virtualenv/cmdline.py [0:0]
def parse_args(self, args=None, values=None):
args = [o[2:] if (o.startswith('-O-') and self.has_option(o[2:])) else o
for o in self._get_args(args)]
args.extend(os.environ.get('DH_OPTIONS', '').split())
# Unfortunately OptionParser is an old style class :(
return OptionParser.parse_args(self, args, values)