Optionally redirect a content to another url?
I think you could handle this in a views row level template file. 

First set up a field for the redirect which is optional. Then add it to your view. Create the appropriate views row template file. In your template file print out the fields individually adding a bit of logic around the read more link:

&lt;?php if ($fields['news_url']): ?&gt;
  &lt;?php print $fields['news_url']; ?&gt;
&lt;?php else: ?&gt;
  &lt;?php print $fields['readmore']; ?&gt;
&lt;?php endif; ?&gt;


Obviously the field names are wrong but hopefully this gives you the idea.