The frugal quantifier means shortest, but still leftmost. You can use a greedy .* at the beginning to consume as much as it can, keep it, and then replace the comma with "and". 
#!/usr/bin/perl
use warnings;
use strict;
use experimental qw( signatures );

sub non_oxford_list($s) {
    $s =~ s/^.*\K,/ and/r
}

use Test::More tests => 3;

is non_oxford_list('A'), 'A';
is non_oxford_list('A, B'), 'A and B';
is non_oxford_list('A, B, C'), 'A, B and C';

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

In reply to Re: Non-greedy substitution by choroba
in thread Non-greedy substitution by Bod

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