Probably not Pope Francis.
Priest: Who cometh here seeking the baptism of icy water?
Candidate: I come here so to seek.
Priest: And why seekest thou such a baptism?
Candidate: To increase awareness of ALS (or he may say "baldness", or "big noses", or any other ailment that afflicts mankind). Also, because I am too stingy to dip in my pocket and send cash to a charity.
I'm used to being humiliated. I can even stick my head in a bucket of water if you like.
Priest: And who wieldeth the bucket?
Wielder: I do.
Priest: Dost thou promise to wield the bucket fairly, taking care that most of the contents fall upon the candidate? And wilst thou endeavour not to splash me?
Wielder: I promise this.
Priest: And who beareth the video camera? (Or he may say "mobile telephone".)
Bearer: I do.
Priest: And dost thou promise to place the fruits of thine efforts on Youtube, that all may see how wondrous are the deeds of the Candidate?
Bearer: I so promise.
At this point there may be a reading from Lamentations 3:54. "Waters flowed over mine head; then I said, I am cut off."
It is advisable to remove the bottles before proceeding.
Priest: Art thou ready to receive the icy water?
Candidate: I am ready.
Priest: Then let it be poured upon thee.
The wielder shall now invert the bucket, and the video camera shall "roll".
Candidate: Eeeek! Owwww! (Or he may use another form of words, such as "Yarooh!" or "Aaagh!")
Priest: Hast thou gotten a good "take"?
Bearer: This I have done.
Priest: Then the deed is done, so let us go forth in gladness.
The procession shall now leave the church, and the candidate shall seek a towel and dry raiment.