http://forums.hak5.org/index.php?/topic/27549-usb-hub-powered-by-wifi-pineapple/#entry210154
Did you read the posts in this thread? I linked you a powered one that does not require any cutting, and a search of the forum will yield you several more..............
The difference in power consumption between a 2 port and 4 is negligible if the other 2 ports are not in use.