View with relationship to custom entity via computed property
Finally figured out a workaround: Pull every needed entity property as a "virtual field" into the node itself.

// define additional property information for node
function mymodule_entity_property_info_alter(&amp;$info) {
  $properties = &amp; $info['node']['properties'];
  foreach (array('myprop') as $property) {
    $properties[$property] = array(
      'label' =&gt; $info['mymodule']['properties'][$property]['label'],
      'description' =&gt; $info['mymodule']['properties'][$property]['description'],
      'type' =&gt; $info['mymodule']['properties'][$property]['type'],
      'computed' =&gt; TRUE,
      'queryable' =&gt; TRUE,
      'entity views field' =&gt; TRUE,
      'getter callback' =&gt; "mymodule_node_property_verbatim_get",
    );
  }
}

// getter callback
function mymodule_node_property_verbatim_get($data, array $options, $name, $type, $info) {
  $myentity = mymodule_get_from_node($data);
  return !empty($publication-&gt;{$name}) ? $publication-&gt;{$name} : array();
}

// obtain the related entity from the node
function mymodule_get_from_node($node) {

  // some custom code to get myentity

  return $myentity;
}


Thus, the properties can be adressed as views fields as well as for any other purposes. It's possible to extend this to access properties of nested entities, too. 

One drawback, however: The fields cannot be used as views sort criteria.