I don't think an outboard broadcaster be rewired to recieve. And if could be rewired, you'd have to leave it to the pro's.
If you absolutely HAD to get an outboard broadcaster, I would strongly recommend the Belkin TuneCaster II. Unlike other broadcasters, you can set your frequency, starting at 88.1 MHz to 107.9 MHz. Plus, you can have up to four presets programmed into its memory. There is a con for the TuneCaster II: Whenever you are not using it, you have to take out the batteries, 'cause the TuneCaster will suck the batteries dry. But, if you mainly use it in the car, Belkin does provide an adapter that plugs into the cigarette lighter socket.
Trust me. I own a TuneCaster II.
400 MHz iMac DV/SE, 120 GB total (with external HDs), 256 MB RAM
600 MHz iMac DV/SE, 80 GB total 384 MB RAM
2 GHz MacBook 13", 80 GB total 2 GB RAM
iPod Photo, 30 GB
iPod Video, 80 GB
iPod Nano, 2 GB
AirPort Extreme with DSL broadband