Gaining

Keep up the gains man. Though you might want to re-think how you put on weight though; being so reliant on sugar for weight gain is a bad idea, it's the largest contributor to type 2 diabetes. Balancing it out with a high fat/carb diet would be a much better way to go.

Sugar intake leads to increased appetite, so you could drink your soda/coffee and the high-fat food will be much easier to put down

I agree with not relying exclusively on sugar, but you can do both. It's very possible that as you gain your appetite for "real" food will go up anyway. No one's said anything about 360-420 pounds yet; you can try to gain a few dozen via sugary drinks and then go from there.