How can I help my horse's tail grow faster?

My thoroughbred had a knot in his tail about 2 months ago and ripped it out on a fence post before I could untangle it. He's got a big muscly butt and his short tail looks awkward. My trainer thinks he might have ripped it from the bone or something and it may never grow back? With or without a tail he's still my beautiful boy! But does anyone have any tricks to helping it grow? It doesn't look like its improved much at all...