I can't seem to make the second lemming bump his head on the second bridgepiece laid by the first, he just keeps on building through it. A way to framestep would be very helpful. It has to be something similar to your diagram though. 36 seconds (the top score) is pretty much exactly how long it takes the main body of lemmings to reach the exit.
I see, I'm kinda afraid something like that might happen. I wonder though, maybe the reason it doesn't work is because the second bridgepiece is simply too low for the PS3's builder game mechanics to detect? If so, I wonder if the following setup (see diagram) might work. This is what's supposed to happen, once again, it may fail spectacularly with PS3 game mechanics:
1) the 1st lemming (A) needs to lay his 2nd bridgepiece just as the 2nd lemming (B) falls off from A's first bridgepiece (ie. B never steps up onto A's 2nd bridgepiece, but that bridgepiece needs to be laid as soon as possible nevertheless)
2) when B lands, immediately assign him builder.
3) hopefully the timing works out such that when B is about to step up, A has just laid his 3rd bridgepiece that B would bump his head on
4) now this part I am most uncertain about: in PC Lemmings, if the builder stops building due to bumping his head onto a ceiling, the game always move the lemming up onto the step he just laid, before doing the turn-around. I have no idea how PS3 reacts in this situation especially since I don't know if it treats the 3rd bridgepiece as a ceiling or a wall (or something else).
But if PS3 reacts similarly to the PC Lemmings ceiling case, it might just be possible for B to start building the yellow bridge in the position shown in the diagram. You must assign B builder immediately after he stops building, not giving him a chance to walk (otherwise he'd get up onto A's 3rd bridgepiece).
5) Another uncertain part is whether B will be able to lay the second yellow bridgepiece in the diagram. The hope is that A's 3rd bridgepiece (in red) is low enough that B will build through it (just like the failure you encountered with my first diagram), and A's 4th bridgepiece (not depicted) is far enough to the right that it is undetectable by B.
6) If the yellow bridge works then once again, one final bridgepiece (green) by a 3rd lemming will create the stack of 5.