Oh, interesting. Here is my solution (the trick that I had been referring to should become obvious):
Let the first lemming walk a ways then make him dig. Make the second lemming fall in the hole and dig also, make the third lemming hit the right side of the diggers' tunnel and face the exit, then dig in between the first two lemmings, freeing at least one (so there are only 2 diggers digging). Raise the release rate to 99. After waiting a bit to get a safe fall height, make the digger facing the exit a basher. Stop the other digger by making him a builder (this can be done at any time.)
Leviathan, I've just downloaded your pack and will take screenshots right away. One note, they are being filed under "levpak1" instead of "levipak1", because that is the name of the .dat file. If this is unacceptable let me know. "levpak1" might sound generic, as in "level pack 1", whereas "levipak1" couldn't be construed that way... but it's your choice, just let me know!