One change and one minor problem with my suggestion.

First, you don't need the second alias, since it's a prefix of the argument name.  Also, HelpFormatter._format_actions_usage ends with a bit of code labeled "clean up separators for mutually exclusive groups"; it removes matched parentheses from the argument names.  :(  I'd recommend that you instead use one of the following (all of which I've tested):

    parser.add_argument('--verbose[main]', ...)
    parser.add_argument('--verbose{main}', ...)
    parser.add_argument('--verbose<main>', ...)