I think this is a bad idea, but if you're going to do it, try this.
Have several friends over to spend the night. Get in your boxers early in the evening, have your usual fun - video games, wrestling, whatever. Before it gets too late, turn the talk to girls and things you'd like to do with them when you're married. After a while, say, 'Hey, you guys want to have a contest?' When they say 'What?', say 'A jerking off contest! Has anybody ever heard of the soggy biscuit game?'
See if anybody else has and let them explain it, and say, "That sounds fun. Let's do it'
If they haven't, say, 'It's a contest to see who can jack off the fastest. You want to do it? I want to.'
When you say, 'Let's do it' or 'I want to', start taking off your boxers like you expect them to join in. However you do this, it would help to talk to one of your friends in advance and tell him what you are going to do, and ask if he would help you get it started by saying 'Yeah, I'm in. How about you guys?' and taking off his boxers.
When you are all naked, that's the time to bring out your biscuit or toast or cracker or even a piece of pizza. Say, 'we all ejaculate onto this and whoever is last has to eat it'. If too many people object or drop out (I would not take a chance on that - no way am I eating another guy's semen), then say, 'Ok, let's have a target contest' and put a bullseye on the floor in the middle of the circle.
I'm sure this has happened, but I think it gets talked about FAR more than it ever happens. It's just one of those gross stories that gets everybody's attention.