Me and my friends just got it today.
Well, this is the second time we've attempted this, first time we spent an hour and a half and got to the end at last, but, no 'Ba-dink' sound. We looked, and we had it on system link

.
So, two or so weeks later we had gotten gold again, and we had experimented off system link for the best course of play. Today, we did it, and got it within half an hour. Thirty minutes. Epic.
What we did, was at the first level of the platform (Just before you meet Johnson) don't go through the door yet, but instead, jump off the ledge just to the left of the door (AKA, keep going straight), there, you will see, nothing. But, look up, if you jump on one of your friends heads, and you jump, then he jumps and you jump again, you will get to the top of that middle ramp, get another guy there and go to the top.
The other two, they will continue the way that your suppose to, but, with far less resistance. It's like, the first guys just erased them! So, that's all that it took. We got it

/