PhotonJunkie

The "File Placement Rules" feature can do this, actually. 
It may require extensive micromanagement, depending on how your pool is setup, but the UI should allow you to easily do this.
http://stablebit.com/Support/DrivePool/2.X/Manual?Section=File%20Placement
 
As for fragmentation, you can defragment the disks in the pool, without any issues.
 
 
 
So that is a drive does fail, you can be certain that you have all of the contents of a particular folder (or none at all). 
 
 
I've been there (not blue ray rips, but re-encoded files), and it sucks.  It may be worth investing in enough drives to duplicate everything.

I would imagine because he said that there isnt enough room to do any duplication
 
so while he wants pooling, he wants individual folders to stay together
 
so if a drive dies.. he will only loose whatever was in the folder on that dead drive (which is not ideal.....)
 
rather than simply losing a fraction of the files in every single folder (which would be a huge pain in the ass)