Does anyone know if there is a solution that allows syncing of music to both the internal and external memory without creating duplicates on either?  Essentially, I'm looking for software that can fill the internal memory with music and then put whatever doesn't fit onto the external memory (in this case, the microSDHC card on my Sansa View).  This seems like a simple thing, but I've actually not been able to find a good way to do it.

 My solution thus far has been to create playlists in WMP that divide my music into to groups by length of song.  This works, but only because I manually chose a lenth that roughly divides the music across the two storage devices in the Sansa.  Of course, this method won't work for an arbitrary collection of songs unless I manually choose a dividing point again.  Most annoyingly, WMP only allows the choice of lengths by the minute when it comes to searching (how hard could it possibly be to allow me to enter a value?) so I can't even choose the best time to sort the music with.  I would be very interested if anyone has a better solution.