If it is cashm then in my OPINION (there is no rule for this) he can give his friend the chips as it is the same as him cashingthem out at the bank and giving his friend the money to buy in with, just a bit quicker. This i have no problem wth, however if he wants to come back into the game it is trickier, as if they start alturnating then you have problems with possible collusion etc.
However if player 1 wants to buy back in pernamentally, then as long as he brings back what he took off (RRoP) then I don't see a problem as he has just lent his mate some cash to play with, withuot going back and forth from the bank to change the chips up. I can see how this would look dodgey so some consideration would be needed.
What normally happens on our tables, is someone gets bored of playing, sells his chips to someone waiting, goes and plays a table game and then comes back in an hour and wants to play again, which is fine as its not two people sharing one stack.
Lewis