Alright, well don't start moaning, I've only done this a few times and its worked fine.
REQs;
Motorbike mount.
As soon as the game starts. get your partner to jump in the motorbike.
Jump around the edges of the ring, so the passenger is INSIDE the wall.
Eventually [hopefully] something will happen [i'm not sure what exactly triggers it], and the partner will be teleported up to the top of the ring and able to meet the other team when they pop out.
This worked for me in 3.2 and I am currently trying to get pictures.