Sync iPhone Without Charging Title says it all. Is there a way to sync an iPhone with iTunes (tethered) without charging it concurrently?

An answer below indicated that this was possible by either modifying or purchasing a modified sync cable. If anyone knows how to do either one, please feel free to answer.
It will likely depend on the pins you are using on the iPhone end. A modified cable should be able to cut the charge sense portion of the signal (or otherwise manipulate the call for charge signal) while allowing the sync portion of the USB signal to pass.