I think they baptised 500 or so this way at the Melbourne International in 2014 - see photos in OP
That sounds like an incredibly high number of baptisms when the trend in recent years is fewer and fewer getting baptized.
yeah, sorry about that
I believe the final count was 695 baptised in Melbourne and a total of 986 with the linked conventions over that weekend
It was an international convention with around 70,000 in attendance - it was HUGE MASSIVE - biggest attendance at the venue in Melbourne etc etc
(That seems about right percentage-wise - I understand that year London had an attendance of around 50,000 and 359 baptised - actually London had so many they continued to baptise people through the opening talks of the Saturday afternoon session