title: Force relationships on django models for models that aren't officially FK related
body: <p>I'm trying to figure out how to get the django admin system to display my models as inlines, when there isn't a direct FK from child to parent model. </p>
  
  <p>I have three models (pseudo code): </p>
  
  <pre><code>class CampaignMain(models.model):
      ...
  
  class CampaignMonitor(models.model): 
      campaign = models.OneToOneField(CampaignMain, pk=True)
  
  class CampaignTransaction(models.model):
      campaign = models.ForeignKey(CampaignMain)
  </code></pre>
  
  <p>So both CampaignMonitor and CampaignTransaction FK CampaignMain, which is the way I need it to be structured.</p>
  
  <p>Here's the bit I can't fathom:  I need an admin page showing CampaignMonitor with CampaignTransaction as inlines.  But when I try this, I get "error no fk in CampaignTransaction pointing to CampaignMonitor"</p>
  
  <p>Is there a way to "force" the relationship just for the admin page? Or is there a generic FK option?  I saw something in contrib/contenttypes, but it doesn't seem to be what I need. Or am I going to have to build a custom admin section to two models in that way?</p>
  
  <p>As always advice is greatly appreciated. </p>
  
  <p>imanc</p>