After i looked into a guys that unlocking their CoC for the first time they have something in common it's their resolve of them willing to sacrifice themselves for their goals.
luffy unlock his CoC cause he wants to protect his saviors even though he knew them for like hours he even go as far as ditching his plan to escape.
Ace stay to fight cause he don't want luffy to get hurt knowing his chance of winning is low.
Doffy refuse to die cause he wants to exact his revenge and kill a lot of people. absolute celestial dragon behavior.
Zoro keep pouring his haki into enma even if it could kill him at any moment.
then we have sanji, with this panel
he's still fear that he cant stand a much hotter flame and he needs a better CoA and Exo
Sanji is still not willing to sacrifice himself to achieve any PU yet.
i think there's more than 1 way to unlock his CoC in this situation
1.Zaza will be his test to his principle of not hitting women and at the same time protecting elbaf from killingham if he's willing to sacrifice this much maybe he'll unlock CoC then start the stronger flame going doffy route of i will survive just to fk you up.
2.Sanji will start producing a much hotter flame that even him cant stand it and start burning himself so he can protect elbaf no matter the cost and unlock CoC with stronger flame going Zoro route if i die i die WCYD.