I over prepared on this map, but if you are worried about the LS then you can dig into the ground and ignore the creeper. Go after the gateway to the left as quickly as you can (before the ground dissolves) because there is no creeper around it for quite a while.

The blasters at the bottom are enough to prevent the creeper from spreading up, even with the gravity, for quite a long time. Then it should be fairly quick if you dig a long way down before attacking the emitters.