Overflow onto SD card?

When synching songs onto my Clip+ 4GB with 8GB external SD card, is there a way to make the playlist simply “overflow” onto the SD card instead of my computer seeing the internal and external memories as seperate entities and duplicating the songs on each?

There may be media manager software (something like Windows Media Player, Rhapsody, Winamp, etc.) that can do this, but I’m not aware of any of them having this ability.

Thanks for the reply!