[Unionfs] Unionfs capability queston

[Jim Kissel]

Google hasn't been particularly helpful in my search for information 
about unionfs.  I have read unionfs-odf.txt and usage.txt (thx Erez) and 
browsed this archive, and have even managed a simple mount via unionfs, 
but I can't figure out if I can use Unionfs to solve my problem.

I'm working a computer with a computer with very restricted disk space. 
  It has several USB ports through which I could mount a drive.  This 
solves the limited disk problem, but doesn't help increase the disk 
capacity of /bin and /lib (and similar directories).

Is it possible using unionfs to mount an directory from one of these 
external sources such that it forms a union with /bin that is 
transparent to the user?  I would like to do similar with /lib

A program on /media/external_dirve/bin would appear to be in /bin and if 
it needs any additional libraries, the ones stored on 
media/external_drive/lib would appear in /lib