It's easy :) Throw the portal on the yellow pad (from a distance) use it to fire on the red switch and your good to go.
You don't need the green diamond. And you need the yellow only to get to the medal.
On my way, hang in there! Just started world 4.
FYI you can move a flaming ball when you throw a sponge into it, which can also result in trapping it in walls ;)
After all these years.... I like this move.
