On Empty Space is hardly a waste, I also found another (other than the one I uploaded) which I think is only possible on Lemini and it’s extremely difficult. It involves building up to the left exit platform from the left using only two builders and you bash once at the top and he’s high enough that he stops. It’s extremely difficult to build at the right spot to make this achievable.
I still don't quite understand the intended solution even after reading it in your help file.

see screenshot. Not too difficult, just a lot of looping around, takes a while; I had only 10 seconds left.

not much difference from part 1 really.
The only difference being, you need to mine, then also bash through the platform where the switch is to ‘waste’ more time for the lemmings to run around since you can’t change the RR in this one.

-you can use up two builders on the top platform where the acid lemmings are, and only two (the maximum you can lose) will die.
-from there you can bash left through the steel over the balloon, then bash all the way across the long passageway and glitch again through so he comes out near the 1-way-wall.
-From there, mine and bash into the holding pit where the water lemmings are to free them.
-then build [over the water] up to the acid lemmings and bash to break the steps you made earlier then free the way for them.

-block the acid lemmings same as above, then build a wall on the left, single out the hero
-then send him down the tall cliff on the left and up then through that seemingly pointless 1-way-wall, then up to the acid and the rest is the same.
Except in this case it’s easier to free the two groups separately.

the level I posted here: http://www.lemmingsforums.com/index.php?topic=563.msg11839#msg11839 is a better example of a builderless level that I've made, I think. I can't remember if I released it as a pack or if it was only as a single level file though. It has some placeholder name like "it's a long way to the top".