The first lemming builds
three times such that he finishes up against the wall. This is just shy of reaching the top - that's fine. Meanwhile, two athletes go over the wall and build a splatform on the other side (first one blocks - the green blocks around the exit are steel just like all other non-yellow blocks in this level). While all this is going on, the 4th and 5th lemmings block immediately under the entrance.
Once all the above is done, blow up the blocker holding the crowd (not the one on the water side, obviously). You then use a bomber at the top of the bridge to trigger the jump glitch, sending the lemmings up to the top. They fall onto the splatform on the other side, and two turners get them to the exit.
For
a variation that saves 35, you instead need to very carefully time the bomber that releases the crowd, such that the lemming that built the bridge can use a digger to trigger the jump glitch.
Unless you already understand the jump glitch fully, this may be very hard to follow, I suggest watching the replay.