Ok, that makes more sense. If you just want to convert "" to "" in the response content, look at the Stream profile in the Virtual Server configuration. You can specify a search and replace string and it will take care of it for you. In your case you might want to include the full hostname in the search and replace to make sure you catch the right string.
You can do an iRule based solution to this as well but if you are just doing a simple search/replace, the stream profile is the easiest way to get it done.
Hope this helps...
-Joe