Besides what tye said in Re^4: GetOpt::Long usage style (\my @a), you can just use an arrayref instead. Obviously the reference operator \ required for scalars can be omitted.

'multi=s' => (my $multi  = [1..3]),
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Same for a hash/hashref. Admittedly it is not quite the same as what one would expect from

'multi=s' => (\my @multi  = (1..3)),
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Which throws an error, which I think is arguably an error in Perl.

BTW, sorry it took me so long to reply, and thanks for adding your point.