I discovered something in the game. I think it can be use full.
When you jump and press B, you make a stomp, well, there is a way for aiming (only close targets) and fall always over them (including allies like the toads or even platforms)
I tried it several times and I'm sure is this way (It does not work always, I need to masterpiece it more)
When you try this, increase the volume of your TV, by that way, you will know if you did it well (as is hard to know if you made it visually only when you are learning - I realized of this due the sound)
Well... you should jump, and the aim with the mote on Mario or Luigi (while in the air) move the cursor around him and then press B. Move the cursor fast but as close as possible to Mario/Luigi (touch him) You must do it fast, its easier if you learn to do it with the mortal back jump (as its a higher jump) and if you can, with Luigi (who jumps higher) Try to start moving the cursor at the very first moment you start the jump, and when you reach the highest you can with the jump, press B (but keep moving the cursor) It will fall on a close enemy or ally) Also, you will heard a different sound.