blurred mist-effect using halo or some other "DOF" technique

Hi, just wondering, after having played with mist whether it is possible by using HALO or some other device unknown to me, if it is possible to blur an object in the background of a landscape(for example)
The thing is that the mist effect works nicely for many things, but it would be nice to blur out a tree in the background, thereby obtaining a DOF experience. Using halo the object is divided into many blurred bits, so I wonder if it could be made into ONE blurred bit instead of several. Because that would solve my problem :slight_smile: