The fastest and most immediate is to make %foo and %bar package variables. Your methods live as package globals, there's no reason their data can't as well. I wouldn't solve this that way though. You're typing a lot of the same things more than once. You also have a bug - you've not accounted for passing in the undef value.

my %Vals;
for ( qw(foo bar) ) {
    my $method = shift;
    *$method = sub {
        my $self = shift;
        my $old = $Vals{$method}{$self};

        $Vals{$method}{$self} = @_ ? $_[0] : ();

        return $old;
    };
}
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Oh yes, I nearly forgot (this is an update). The destroy method. Also, explicit return values are a virtue. It gives you something to expect instead of just having undefined behaviour (which leaving that delete on the end would certainly have done).

sub DESTROY {
    my $self = shift;
    delete $_->{$self} for values %Vals;
    return;
}
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