I just figured this out (by mistake)! If you skip the coins or collect less than 5(?) on the first part (make sure you get Yoshi, though), you will come to the section with flying turtles and a lot of slants. You pretty much need to rush through this section with no dilly dallying to get to the second ending. I'm not sure exactly what amount of time you are allowed to spend, but if you rush through except for two almost necessary pauses, you'll make it.

to get to the second level of chocolate island 2 you get alll the coins (keep hitting the question box that gives more than one coin and theres a secret box just next to it if you jump up). go through the level once getting all the coins you can and once without getting any of them and you'll have the two exits.