Blockforms code to save the current page NID to a entityreference field in the embedded form.

gistfile1.php

<?php
/**
 * Implements node_presave to attach the current node's nid as an entity reference in the node being saved in a block form.
 * This code requires 'journal_entry' form to be embedded on a 'course' with the formblock module and the journal_entry type must     
 * have an entity reference field called 'field_course_reference'
 */
function ucg_node_presave($node) {

  $journal_wrapper = entity_metadata_wrapper('node', $node);
  if($journal_wrapper->getBundle() == 'journal_entry') {
    if (arg(0) == 'node' && is_numeric(arg(1))) {
      $course_node = node_load(arg(1));
      $course_wrapper =  entity_metadata_wrapper('node', $course_node);
      if($course_wrapper->getBundle() == 'course') {
        $course_nid = intval($course_wrapper->nid->value());
        $journal_wrapper->field_course_reference->set($course_nid);
      }
    }
  }

  return $node;
}
?>