#file: Foo.pm
package Foo;

*do_something = &make_do_something( 'foo' );

sub make_do_something {
    my $name = shift;
    ## In my real code, I have other interesting params here
    ## that gives my sub the information to do the
    ## things that each class knows about.
    return sub { 
        my $self = shift;
        if ( $name ne 'foo' ) {
            print "Not foo\n";
            $self->SUPER::do_something();
        }
        print "Foo $name!!!\n";
        return 1;
    }
}
__END__

#File: Bar.pm
package Bar;

use base 'Foo';

*do_something = &Foo::make_do_something( 'bar' );

sub new { 
    bless {}, shift();
}
__END__

#!/usr/local/bin/perl
#File: foobar.pl

use Foo;
use Bar;

$b = new Bar();

$b->do_something();
__END__