#!/usr/bin/env perl -w

use strict;
use warnings 'all';

BEGIN {
  push @INC, sub {
    shift;
    my $classfile = shift;
    if( $classfile eq 'My/Missing/Module.pm' )
    {
      (my $classname = $classfile) =~ s/\//::/g;
      $classname =~ s/\.pm$//;
      my $code = <<"CODE";
package $classname;
sub hello {
  return qq{Hello, \@_!\\n};
};
1;
CODE
      # You have to return an open, readable filehandle:
      open my $ifh, '<', \$code;
      return $ifh;
    }
    else
    {
      return undef;
    }# end if()
  };
}

# Load up a non-existant module:
require My::Missing::Module;
print My::Missing::Module::hello("Studly");
# Output: "Hello, Studly!"