Actually there is a much simpler and non-magickal way to handle my requirements since I'm already using Moose. I will just create a Role method that takes a shortened package name and does the loading of it:

my $instance = 
  $self->gnew(LastPartOfLongPackageName, @args_to_constructor);
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And the code is non-magickal:

package XML::Quickbooks::Util;
# ABSTRACT: various utility functions

use Moose::Role;

sub gnew {
  my($self, $pkgtail, @constructor_args)=@_;

  use Class::MOP;
  my $class = "XML::Quickbooks::Generator::$pkgtail";
  Class::MOP::load_class($class);
  $class->new(@constructor_args);
}
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