A bit trickier than I originally thought. What I didn't expect was the need to use the :lvalue on both the listifier and constructor. 
#!/usr/bin/perl
use warnings;
use strict;
use feature qw{ say };

{   package L;
    use overload
        '+=' => sub {
            my ($self, $inc) = @_;
            $_ += shift @$inc for @$self;
        };
    sub new :lvalue {
        bless $_[1], $_[0]
    }
}
sub L :lvalue { 'L'->new(\@_) }

my ($x, $y, $z) = (10, 20, 30);
L($x, $y, $z) += L(3, 2, 1);
say "$x $y $z";  # 13 22 31

[download]
You can use [3, 2, 1] on the RHS, as well.

map{substr$_->[0],$_->[1]||0,1}[\*||{},3],[[]],[ref qr-1,-,-1],[{}],[sub{}^*ARGV,3]

In reply to Re^2: A list assignment gotcha by choroba
in thread Not understanding 2 sentences in perldoc by Anonymous Monk

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