Ok, yeah. I remember the level. Yeah, the solution is quite similar to "Tightrope city".
Make the fourth lemming a blocker right when he lands from the trapdoor. When the first Lemming reaches the "gap", make him a builder. Then, make the third lemming a blocker so that, when the builder will end building, the top of the stair will be right above the blocker's head for the lemmings to pass. With the second lemming, just build to the exit.
I don't remember if you also get some bashers, but if you have some, you can give them to the first lemmings that are coming to the exit, passing the blocker, to slow them down.