Instead of using the drillers, you can use the climbers. First, get a climber to go up the short side and start building to the right. Before hitting the flames, turn it into a blocker. Then make another lemming climb up the short side, turn at the blocker and build back to the left until nearly at the flames on the other side. Turn into a blocker again. Make a third climber to go right again, let it climb to the top, drop down onto the centre platform, climb over the flames on the other side and parachute down. Now you can create a staircase up the short side to get all the other lemmings to join and parachute down.