Grapple hook on to it. Hold to Reel yourself in, continuously feeding it while staying grappled. Rarely will hit you as it spins trying to reach you. Grapple wont releas because as long as you dont hit it, it wont count as combat
Diplo's are super tanky. Everyone doesnt realize this is now the BEST bullet tank in the game. When heath is low, sprint out with no problem. Unlike the bronto, the Diplo is very fast. While passive taming, realize that first feeding you have about 15 minutes until next feeding. Then all quick after that.