What I do is I run while already holding 2 then press 4 when I reach the enemy in the air. Maybe don't let the enemy fly too far away after bounding because it'll be hard to catch up with the air grab.
It depends whether you're trying to do WR 2+4 or iSW.
The former is easy. You just go into a full run and then hit 2+4.
iSW (instant shining wizard) is a bit more difficult and takes some practice. The most important thing to remember is that you can ONLY buffer the FIRST f input. Every other part of the input has to be performed after the animation of the previous move.
To practice this, try doing a jab (or any other move) then pressing the first f before the animation of the jab ends, and then pressing f just after the animation the ends. If you do it correctly, you'll instantly dash after the jab.
Once you get that down, just add another f+2+4 on to the end, and thats it, you just learned iSW. Also good for tick throws.
You can also just do fff really quickly after the jab (or whatever) ends, but I find this more difficult personally.