Was your solution something like this(highlight this to read it)?
Make the first lemming a digger near the edge. The second lemming becomes a blocker - this has to be positioned at the very furthest right it can, while still allowing lemmings falling from the entrance to walk past. The third lemming becomes a miner as soon as he is far right enough to avoid freeing the blocker with his tunnel. Bash under the lava as soon as possible. Make the first lemming mine through the vertical pole. Whatever lemming gets to the wall first, make him a climber. Mine through the vertical pole that was mined through just before(but this time, obviously, you are mining near the top), then make the lemming mine as soon as possible after falling off the diagonal bars. Once he finishes, have a lemming build when he is walking right and between the furthest left point of the gap the mine created, and the halfway point of the gap. The climber should turn around on the blocker about the time Lemming 66 comes out. Lemming 67 mines as soon as he lands to free the blocker. All the lemmings should make it to the exit just in time.
