If you're the host of the game and you're a good jumper, then only one person is needed to jump the map. Let the host jump to the other end alone. Once he's inside, let one other member go into any entrance portal. The timer will start. After it's up, the host will lead the party to the portal he went in.
If the host is not a good jumper, then you can gamble. It's a 50-50 chance. Let the first person who got into the room be the jumper. When he gets across, let anyone other than the host get in the entrance portal. The timer will start. It's a 50% chance you're whole party will continue to the next map. If not, then let the second person who got into the room be the jumper. It's a 75% chance the party will move to the next map. If not, then the third jumper is a 100% chance -- but through this gambling strategy, it might be better to have two jumpers to begin with.