I thought about a tape adapter...or a FM transmitter. Now I want a bluetooth adapter. Just plug them into the RCA inputs for your deck. Wireless audio! I'm planning on buying one for my house and one for my car. ...I haven't really done this yet, but eb says it should work. Here's a few models, let me know if you see cheaper/better models...
Amazon.com: Iogear WIRELESS BLUETOOTH AUDIO ( GMA201 ): Electronics Amazon.com: Bluetooth Stereo Gateway DC800 Bluetooth Adapter for Home Stereo: Electronics