Changing the source parameter for a Facebook comment box

Question

I have a Facebook iframe application. I have applied Facebook commenting on this.

Right now the comments which are posted on my wall display the source parameter and title parameter (a clickable URL) the same.

I wanted the source parameter to display my application name, and clicking on the title will redirect the user to the page specified.

My code is

<fb:comments 
  xid="'.$xid.'" 
  title="My Blog Comments" 
  width="400px"
  url="'.$postURL.'">
</fb:comments>