Not really backflush, but the governor can be removed and cleaned.
With the valvebody off and the servo out, you could probably blow out the passages, but it would only be a foot or so of passages.
Usually it works to just let the stuff end up in the pan and then change the fluid and filter. (If nothing sticks that is)
I have had to pull and flush out valve bodies from stuck shift valves if stuff got in them.
