You can modify them by using the 5v or 12v feed from one of the balum connectors. If you want to make a nice mod you can use solder. You should be able to put 2 fans on 1 and 3 on another. Dunno if I would put all 5 on 1 connector.
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The molex connectors is the better choice. That way you dont have to worry about how much power youre pulling.
If you dont mind spending more money you could buy a fan controller add-on. I bought this one for my boss's computer:
ENERMAX's Aluminum UC-A07FATR2 (BLACK) Multifunction Transfer Panel. Features: Over Heat & Low RPM Alarm. Dual Temperature Monitors. Dual Fan Speed & Temperature LED Display. Fan Speed Adjustable. Fits In Standard 5.25 Drive Bay. 2 USB2.0 Ports. 1 Firewire Ports. (IEEE 1394)