Fun 28 improved to
4 builders. Sadly, 100% doesn't seem likely, since the key builder-saving move involves using a basher or miner on a bridge in progress, and either way it looks like that lemming is toast (literally
) due to the lava below.
It is possible, with better timing, to make the miner glitch-cross the gap into the pillar, but that leaves a gap in the bridge, which presents its own problems. But still, that's probably the only hope of 100% here.