I got this with some monkeying around:

use Data::Dumper;
package Foo::Empty;
package Foo::OneVar;
$one_var = 'foo!';
package main;

my %done;
sub seek_destroy {
    my ( $name ) = @_;
    return if $done{$name}++;
    foreach my $package ( grep { /::$/ } keys %{$name} ) {
        print "$name$package\n";
        print "!!! $name$package" . "DESTROY!!\n"
            if exists ${"$name$package"}{DESTROY};   
        seek_destroy( "$name::$package" ) if defined $package;
    }
}

seek_destroy( 'main::' );
[download]

It finds both "Foo::OneVar" and "Foo::Empty", and it sees the DESTROY methods of Data::Dumper and main::Regex. It spews warnings like crazy, but I can polish that up later.