Well, if I were you, Id enabled Dynamic Resizing, and have the centroid of the pyro sim follow the bounds of your source, then it should dynamically track according to the field you specify.
You mean after it's simmed? You bring it back into an object with a DOPs import field SOP, and then at the /obj level, hit esc and ENTER in the viewport and you should be able to translate it around.
Sean Lewkiw CG Supervisor Machine FX - Cinesite MTL