This is a circumstance where time magic may com in handy. You're fighting one of those petrifying green dragons that appear in the same forest as Yuffie. One of them starts the petrifying countdown on lets say, Vincent. Cloud uses manipulate on it. While Cloud's ATB guage is filling up the other two kill the other dragon. Cloud then uses then uses the manipulate command to start the petrifying countdown on the dragon. Then lets say, Tifa uses haste on the enemy, which causes tha countdown to go down quicker than Vincents, and therefore not excluding him from earning any exp. (BTW this actually happened to me )