Nvm I got it. For anyone that's also wondering, you have to touch the loading area with an x coordinate of 09FF. (Not very difficult with a tas editor and RAM watch.) From there, jump at exactly the frame you gain control of your character after the fade in to gain a boost to land on a cloud platform. Quite a peculiar trick.

I saw on Jabem's 100% run he managed to skip the vertical section of 2-1 after jumping off of the vine. What trick is used there to be able to spawn at the top?