Bonus (got the idea by reading tybalt89's version)

sub Invoker::first    { shift; &first_callback }
sub Invoker::last     { shift; &last_callback }
sub Invoker::AUTOLOAD { -1 }

sub invoker 
{ 
  my $name = shift; 
  Invoker->$name(@_); 
}
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Edit: Actually if you ignore the first parameter of the callbacks, you can just use the symbols table as the containing hash and use the method above :)

use strict;
use warnings;

# Callback functions ---------------------------------------

sub first_callback {
   my (undef, $z) = @_;
   print "in first_callback, z=$z\n";
   return 1;
}

sub last_callback {
   my (undef, $z) = @_;
   print "in last_callback, z=$z\n";
   return 2;
}

sub default_callback { -1 }

# Dispatch -------------------------------------------------

%Dispatch:: = ( first => *first_callback,
                start => *first_callback,
                last  => *last_callback,
                AUTOLOAD => *default_callback);

sub invoker {
  my $name = shift;
  Dispatch->$name(@_);
}

# Main program for testing ---------------------------------

for my $name ( qw< first start last fred > ) {
   my $rc = invoker( $name, $name . '-arg' );
   print "$name: rc=$rc\n";
}
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