I've noticed that you can shimmy into the portal on the left side, which seems like it should be part of the solution. Assuming my last attempt had the wrong idea of digging through the splat zone to enable the top lemming to fall safely through (because then both lemmings end up on the bottom, and after your last fix, that's game over), then it must be about using the builders to build a splatform for the top lemming. My idea was to have a lemming building to the left underneath the drop point where the button is, while the other lemming digs down to the bottom, underneath the bridge. The builder would then go back to the portal (using another shimmier to get on top of the platform to the portal then a second shimmier to enter the portal. He then lasers his way through to the button and the bridge he's built safely catches him and he walks to the right, over the hole made by the digger. Meanwhile, the lemming on the bottom uses a shimmier to cross the gap, lasers up to the left, so the top lemming walk down the lasered path and use the final shimmier to reach the last button and that exit. However, all this is scuppered by the fact that the builder dies in the splat zone when he's finished building up three bridges and I just can't see a way around this! It HAS to be 3 bridges high otherwise it won't prevent the splat. Argggh! This is definitely harder than your other two levels in this contest. I feel like I must be close to the solution here but I can't see a way to build the splatform and have the builder survive!

Unfortunately your solution is a backroute. You're right that I'm trying to force the player to use both exits though. It's required by the rule! 

I guess you're trying to force the player to use both exits, rather than just one?