Okay, more like his backup macro rig since he too already has the MT-24EX. Again, a single 270EX / 270EX II is used here.
The speedlite is placed upside down/belly up, like what I mentioned here.
All he needed were some adhesive-backed velcro, and a lens hood.
If you have a 270EX II and a newer body such as the 60D, 7D, 600D, you don't even need the OC-E3 cord as you can trigger the flash wirelessly using your built-in / pop-up flash.
Make sure the lens hood is not too long that it exceeds your minimum working distance at 1:1. For example, if you are using a Canon 100L with a minimum working distance of 5.9 inches at 1:1, the front end of your lens hood should be at least an inch or two shorter so your flash won't overshoot when tilted all the way down.
For more info, head on to Adrian's blog post.
More macro rigs here.