Everything I read about Xylocaine use in Nevada is that it is only not allowed on Fight Night. If he used it on fight night he would be caught (just like Golata was when he fought Lewis).
You didnt see PBF injecting anything on ANY episode of 24/7 I remember the episode you are refering to and he put them in some clay liquid type of substance.
Not if he was super clever about it! Hey, the Pac-man was on roids for every fight, yet he somehow passed all the drug tests (and we know for a fact that he has been on roids since the age of two). So obviously Pacquiao and Mayweather know how to get around the officials...