TuneStage will fit all-size iPod devices using the dock connector, but the device will not ship until late July.

The TuneStage for iPod

Priced at US$179.99, the TuneStage can transmit from up to 10 metres (the limit for Bluetooth connectivity) and should transmit through walls, ceilings etc.
Power for the transmitting device come straight from the iPod itself, so no additional cables are required at the iPod end. The device has a low power consumption of less than 40mA.