777 starts BOTH engines simultaneously.
I'm sure it can, but does any operator do it as part of their SOPs?
Delta used to start both on the push, invariably when the tug being used was one of the weaker ones, and the push back included several tight turns. Depending on how quickly they spooled up, it made things "interesting" on occasions!
On a couple of occasions, I managed to "persuade" the crew to hold the start till the push was completed, as I knew that if they got both turning before we got to where ATC wanted us to be, there was no way that the tug would get it there, it just didn't have the power to fight both engines.
757's used to be interesting in that respect as well, I'm not sure if it's the older design or what, but they always seemed to spool well above ground idle before settling back down to a much lower N1, which again could make push back a little more than interesting.
Classic 747's were the other extreme, the headset man ended up waiting by the nose gear for ever as they spooled up all 4, and one operator required a confirmation for each engine that the fan was turning before they'd continue the start, which used to cause all sorts of problems if the headset that was being used was the normal pushback headset quality. Trying to be heard above the howl of 3 engines live and one just spooling up was sometimes quite challenging. I never did find out why they had to get the headset man to confirm rotation, as it was only one operator that did it, and we didn't get much chance to talk to the crews other than during push back.