If you stand in the perfect spot between its 2 front legs the diplo will constantly try to "attack" you but won't knock you back nor reposition itself to get a better chance of "attacking" you so if you have a stack of mejoberries you can feed it once, afk until the first interval finishes (this can take anywhere from 24 minutes up to an hour and 15 minutes if its a level 150) then after that you can feed it every 43 seconds until its tamed. If you use mejoberries the taming effectiveness will decrease by so little that if you are taming a level 150 you will still gain the 74 levels with 99.4% taming effectiveness. However if you are playing multi your diplo will instead gain 72 levels which is still good.

This method works because there is a small blind spot near the diplo's 2 front legs that is WITHIN its attack range but OUTSIDE OF its attack aoe.