Have you checked what seem to be at least half a dozen possibilities found in the doc? Most require creating a handler, but that should be simple enough for your example case. Of course, if your example is not the real usage, the balance of this node is probably unhelpful.

Also, see,

pass_through (default: disabled)
With pass_through anything that is unknown, ambiguous or supplied with an invalid option will not be flagged as an error. Instead the unknown option(s) will be passed to the catchall <> if present, otherwise through to @ARGV . This makes it possible to write wrapper scripts that process only part of the user supplied command line arguments, and pass the remaining options to some other program.

That/s pretty far down in the doc; the others (left as an exercise for the SOPW) are found in earlier parts of http://perldoc.perl.org/Getopt/Long.html (but don't be misled by the earlier section on negation, which deals with negating built in options.