just like he hid in luffy's ship he can hide in some marine ship in a container in basement etc, and okay karbue gave him food whatever but kizaru putting Bonney in a safe place is a stupid effort as it will only save her for some time, its not like gorosei will give up on her, so if he really want to save her either he has to fight or help luffy, which maybe he didn't but that is the only option he have, and what supports this is kizaru was thinking about it in that chapter and prolly wanted to save them and then luffy got food and then he was sitting silent with "..." just after gorosei asked who gave luffy food, so I mean there is a possibility, and yeah ig karebou hiding in a ship is actually really risky but its less risky than coming Infront of a admiral and gorosei, whereas he has more chance in hiding cuz he doesn't have to come across the gorosei, admiral and other people you mentioned cause they dont go to all ships, just choose a safe one and you're set