How about this for a rule:
3 appeals each, every unsuccessful appeal results in the teams losing an appeal.
TO appeal, players of a team must tell the captain what happened, and he alone must make the appeal, no-one else.
Minimum time added on per appeal is 1 min, unless the appeal takes longer (This will cut out time wasting apppeals).
Appeals can only be made at a stoppage in play, therefore the game is not disrupted.
If play contunies, and an appeal is successful, the time from the continued play must be added on.