define a new method to create a through model

src/Illuminate/Database/Eloquent/Concerns/HasRelationships.php

@@ -115,7 +115,7 @@ protected function newHasOne(Builder $query, Model $parent, $foreignKey, $localK
      */
     public function hasOneThrough($related, $through, $firstKey = null, $secondKey = null, $localKey = null, $secondLocalKey = null)
     {
-        $through = new $through;
+        $through = $this->newThroughInstance($through);
 
         $firstKey = $firstKey ?: $this->getForeignKey();
 
@@ -387,7 +387,7 @@ protected function newHasMany(Builder $query, Model $parent, $foreignKey, $local
      */
     public function hasManyThrough($related, $through, $firstKey = null, $secondKey = null, $localKey = null, $secondLocalKey = null)
     {
-        $through = new $through;
+        $through = $this->newThroughInstance($through);
 
         $firstKey = $firstKey ?: $this->getForeignKey();
 
@@ -759,6 +759,17 @@ protected function newRelatedInstance($class)
         });
     }
 
+    /**
+     * Create a new model instance for a through model.
+     *
+     * @param  string  $class
+     * @return mixed
+     */
+    protected function newThroughInstance($class)
+    {
+        return new $class;
+    }
+
     /**
      * Get all the loaded relations for the instance.
      *