Wait for them to separate if they're in a pack. They'll probably aggro onto so many different things at once that one is bound to get left behind eventually. Take the opportunity as soon as you can, because they can join back up to the pack if they get close to the others again.
Just tamed a level 122 on Dead Island no kibble and only a few narcs on me. Had to fight off a scorpion and a sabertooth to keep from it waking up. As the tame was close to finishing I was attacked from behind by two scorpions and they knock me out. As I'm getting attacked by them and I am sure that I am a goner, the raptor tames, gets the them off of me, and kills both of the scorpions. I wait in horror as my consciousness returns, hoping that I am not going to die to a patrol. I didn't, and I turn around and see a Rex almost close enough to aggro me. I put my raptor on follow ran to my raft, and escaped the island as the Rex was chasing me. I named him Saving Grace on the way back, but as I am passing the swamp, a sarco attacks my raft. It knocks my beloved raptor off, and it was swarmed by the sarco and a group of megapiranha. I try to call it to follow, and it dies almost instantly. I am utterly devastated and heartbroken...... :'((
Try to stay in flat open land, this allows you to easily snare the raptor with a bola. Approach slowly until it runs straight at you then throw the bola at it. Once hit with the bola you can easily KO it using any method you choose.
Use parasuar kibble for faster and higher level tames if possible since you need less than 30 kibbles for a perfect 100+ level tame. It may also be easier at lower levels since gathering meat can sometimes be difficult and parasuars are easy tames.