I played around on the map over the weekend (I can't leave it alone...). I did manage to survive for 84 minutes (about 4 hours in real time) by air-bridging that top left ridge. But I finally quit as I couldn't find a way to advance off of the ridge.
The trick I found is to park OC between the upgrade and the bump in the ridge. Grab the upgrade and start building collectors, reactors, and mortars on the ridge. Sit there as long as you can, until the creeper starts injuring OC, then start the tedious air-bridging. Reactors seem to add more "oomph" when air-bridging - at least to me it seemed like they "added" proportionally more to the meager power collection than the collectors. I mean, I know a reactor adds more than a collector when OC is on the ground, but when air-bridging, the collectors seem to barely add anything, but a reactor adds a good bit.
I couldn't figure out a strategy to take out enough creeper to get a blaster on the valley floor. Even using a drone on the left side and "flying in" two mortars on the right side didn't reduce the creeper enough to where a blaster could clear out an area for itself on the floor. It's just too much creeper, not enough energy, and the emitters are so high that gravity is pulling the creeper down under pressure (that's how I refer to it).
my guess is that the guys who did manage to beat the map (and in 9 minutes) must have air-bridged up that left-central ridge somehow and gotten a foothold on top and capped off that 2nd emitter. I've tried a few times, but haven't had any success yet.