Quick throw-in backwards

One of the possible changes to the law being tested at present is the idea of allowing the quick throw-in from touch to be backwards instead of straight. Peter Shortell of Cheltenham has questions about this. I understand that thought is being given to allowing a quick throw-in to be thrown to a team-mate well behind the point where the throw is taken from. This in itself seems to be a sensible relaxation of the law. but what about the opponents? Where can they stand? Is there an offside line at a quick throw-in? The law does not say - so presumably not. Is a player allowed to stand in front of the thrower near the touch-line so as to hamper his throw? The consensus locally seems to be that he is "preventing the ball being thrown in 5 metres". Either that or 10.4 (k)! [Law 10.4 (k) Acts contrary to good sportsmanship. A player must not do anything that is against the spirit of good sportsmanship in the playing enclosure. Penalty: Penalty Kick]