Module::Pluggable::Object and Class:MOP should be a good start. There's an example of doing this in the new Catalyst book. Something along the lines of this (not-tested code) should work

  my $mp = Module::Pluggable::Object->new(
    search_path => [ "/path/to/classes" ]
  );

  my @classes = $mp->plugins;

  # choose which class from classes

  Class::MOP::load_class( $class );
  return $class->new;
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Depending on how your search_path is, you may need to muck with the class name before calling new (like strip off the leading path).