What limits, if any, apply to participation of outside agents in retrieving a ball that has left the field of play and/or expediting the process of returning the ball to play?

Example: In a U-19 boys game the red goalkeeper collects the ball near the top of his own penalty area and kicks it high and long toward the blue goal. After the ball has been kicked, Red players R1, R2 and R3 streak across the halfway line into the blue half, hoping to collect the ball. They run past B1, the lone Blue defender (other than the keeper) in the Blue half. B1 manages to settle the kick from the red keeper, then kicks it sharply toward the touch line where the Blue substitutes, team officials and spectators are standing. B1’s intent is to give his teammates time to return to the defensive end while the Red team retrieves the ball and executes the throw-in. However, an outside agent (substitute, team official or spectator) catches the ball on the fly about 10 feet outside the touch line and chest-passes it briskly to R4 who has just left the field where the ball went into touch. R4 receives the ball and immediately executes a strong throw-in toward R1/2/3 who manage to score. What should the referee do?

Related question: Under what circumstances, if any, can/should an AR arrest a ball that has passed into touch in his immediate vicinity?

USSF answer (February 5, 2011):
Given the particular questions you ask, the answers are:
1. There are no limits unless the “helpers” are not helping expedite the restart. If the “helpers” are delaying the restart, the referee must step in and put an end to it. (Remember no cards may be shown to coaches or spectators unless the rules of the competition allow for that.) The referee must also add any time lost because of the delay.

2. Unless the ball is about to fall into the clutches of greedy alligators or disappear into a wormhole, there is no reason for the AR to touch the ball in any way. Seriously, the AR should act only if needed to protect himself from being struck. It is almost instinctive (particularly if the AR is a former or current player) to want to stop the ball in an effort to be “helpful,” but this is a misplaced act of good will,because in doing so the AR has actually helped the team with the throw-in to restart more quickly that might have otherwise been the case. And if the AR fails to do the same thing for the other team at any time for any reason, they may think the AR is favoring their opponents. Furthermore, stopping the ball draws attention away from the AR’s main, Law-mandated responsibilities.