I’m pretty ham-handed when it comes to soldering and disassembly but it might be cool to give this a go. Essentially you tear down a Bluetooth headset and cram it into the bottom part of a 4G or 5G iPod. He also added the iVue clear front panel to make it just that much cooler.
He also recommends a CF adapter for the hard drive to save space.
Bluetooth 5G iPod – Finished! [iPodHackers]