You probably want to do this:

#!/bin/env perl

use strict;
use warnings;

my ($a, $b, $c);
$a = $b = $c = 0;
foreach my $v (qw/a b c/) {
    func($v);
}

sub func {
    my $v = shift;
    print "v = $v\n";
    eval '$'.$v.' = $'.$v.' * 2';
}

print "$a $b $c\n";
[download]

It's completely hideous, but it works as long as func() isn't defined in another file.