Are you sure about this? I just read that most of the laptops have an esata port that only provides 5v, but esata ports on desktop mobo usually can provide 12v, then their technical name go to eSATAp ( powered) . On ASUS the eSATAp is called "eSATA On the Go"
I'm pretty sure. ASUS don't specify it, but if you check the manual they mention that a cable able to provide 5V is necessary.
It's the same for all ASUS boards that feature the eSATAp ports (power over eSATA, eSATAp or eSATA on the Go it's the same thing).
That cable will work as long as it is under 2 meters any longer you'll need more power, this board supports SATA on the go, the shorter the cable the better I have the same M/B,, I found one of these Thermaltake Blacx (on EBay for $19)
It works great it does have the 12v external power supply, I was going to go the same route as you but they wanted $15 for the cable and this dock is nice it has a power button and it works just like a flash drive, also I transferred 20Gigs of music in 3mins 15 seconds from my main drive.