OSxWiFi has such a kit using the BCM94360CD card, and yes it DOES require power. They have a special cable made using USB to do that trick. However its a little expensive at 109usd.
It seems that in the iterations I've seen of these upgrades, folks splice into the Bluetooth cable to get power, D+ and D- signals. There's a post that shows the mini PCI-e mini card adapter having wires soldered to the pins to capture power D+ and D-.
There's also a new adapter which has an internal USB cable, with power pins, and the needed connection for the card to input D+ and D-. With a pin connector at one end, raw wire at the other, which will plug into the adapter card you place the 94630 card into. Pretty slick! It makes the fix just like the OS-X WiFi product. I'll report that after I've done it and have it all working.
I'm also working on a mini PCI-e doubler so you can do the WiFi fix on one output and use the other end to have a SATA interface for another drive. I need to talk to an electrical engineer friend and find out it the data rate of the mini PCI-e in the late 2009 iMac will support SATA III for full speed transfers or only SATA II.