This relies on having some separator, 'x' that is sure not to appear in your data. YMMV

#!/usr/bin/perl
use strict;
use warnings;
use Data::Dumper;

my %hash = (
   a => ['1', '2'],
   b => ['2', '3'],
   c => ['1', '2']
);

my %temp = map {(join 'x', @{$hash{$_}}) => $_} keys %hash;
my %d_duped = map {$temp{$_}, [split 'x', $_]} keys %temp;

print Dumper \%d_duped;
[download]

Cheers,
R.