Convert former embedded PHP code into a custom block module?
I don't really think embedding a node form in a node view is good in terms of performance because the entire node form needs to be rebuilt, and it can interferer caching mechanisms as well. Probably a ctools madal form with Ajax will do the job better. 

You can define blocks in your site using a custom module. Panels will pick them up without any further integration. 

function MYMODULE_block_info() {
  $blocks['MYMODULE_post_node_form'] = array(
    'info' =&gt; t('Add new'),
    'cache' =&gt; DRUPAL_NO_CACHE,
  );

  return $blocks;
}


function MYMODULE_block_view($delta = '') {
  $block = array();

  switch ($delta) {
    case 'MYMODULE_post_node_form':
      module_load_include('inc', 'node', 'node.pages');
      $node_form = node_add('post');
      $node_form['buttons']['submit']['#value'] = t('Save and add new'); 
      $block['content'] = $node_form; // No need to render() here. Will happen automatically.
      break;
  }

  return $block;
}


I'm assuming you know how to create a basic module with an .info file, change "MYMODULE" to the module name of your choice and how to install them. 
If everything went OK, you will see the "Add new" block in admin/structure/blocks page and in "Add content" form in panels.