Instead of having to deal with another cord hanging from the flash (external power pack already requires a cable) and everyone has problems with the Canon Off-camera cable shoe, I like to mount my flash on my big lens without the need for another cable. I have the IR controller and am currently using one of the "feet" that comes with the 580 flash to attach it but am looking for something more durable.
You're really better off just getting one of the better quality Promaster-brand ETTL cords from Birds as Art. We have a thread going here: http://www.birdphotographers.net/for...ead.php?t=9438. I also own as STE-2 but I use it to control Speedlites mounted on light stands. I have used it for the purpose you describe and it works, but it's really not ideal. Plus its nowhere near as durable as any of the other gear for wildlife photography.