(Edit: I don't believe _dbh goes away before $self does, I think DBI is unloaded before the global cleanup happens; that's why I'm suggesting this END{} fix...)

Hmmm, you don't need the total encapsulation features of the FlyweightWrapper, either...

I'm betting packages get unloaded correctly. What happens if you add a hash at the package level in your class called instances, and do this:

# private hash of instances
my %instances;

#...
sub new {
    # ... build up $self, bless it, do whatever
    $instances{$self}=1;
    # ... whatever else you need to do...
}

#...
sub DESTROY {
    # don't double-destroy
    return unless $instances{$self};
    #... do whatever
    $instances{$self}=0;
}

END {
   foreach my $instance(keys %instances) {
       $instance->DESTROY() if $instances{$instance};
   }
}
[download]

Offhand, I can't remember whether calling DESTROY directly is ok or not, but if not, you could get the same effect with a helper sub that DESTROY calls.
--
Mike

Edit: I forgot to check $instances{$self} at the top of DESTROY