title: add model relationship without save
body: <p>I have the next relationship <code>User hasMany Contacts</code>.
  In normal situation is use <code>$user-&gt;contacts()-&gt;save($contact)</code> to add and save a contact to the user, but I need to associate contacts to users without save the models (User and Contacts).</p>
  
  <p><strong>edit:</strong></p>
  
  <p>I need to build a plant that receives one of such methods and return an XML a collection of templates, only in some of these models will be stored at postiriori.</p>