They might actually have to be dead before it works.
We know from Ceasar's slime that when a fruit user dies, a normal nearby fruit just spontaneously becomes that fruit. Maybe if you take a bit out of them right after they die, it passes to you instead of to a nearby fruit.
Although, if he knows that much about the workings of fruit, it would probably make more sense for him to have just been carrying a fruit with him to eat once it turned into Whitebeard's fruit...
I dunno man. At that point, someone had punched a volcano through him. A bite mark might have been insignificant.
Eh, that's all Haki and shit. It goes away once he's dead.