You don't need to hack the case up to put a 2.5" in, it just sits in a gap above the drive bays but below the optical one. That said, the above is pretty neat.
EDIT - AND, the above could fit x2 3.5" and still leave space for a 2.5" in the gap. Result!
Pic to show where the 2.5" can go from some guy on the unRAID forums:
http://i.imgur.com/r2Vcj.png[
Just means using a molex to 3 SATA instead of 2, so that's a total of (using unRAID), 1 cache, 1 parity and 5 for usable storage. Nice suggestion! The only thing, as someone else has said in the AVForums thread, is that does this bracket work with the larger drives (i.e. 2TB), since they have more platters and are taller? Derp, also forgot I would need moar SATA ports, since there's only 5 + the eSATA...[/QUOTE]
The bracket if you look closely has 2 sets of holes one above the other to allow different spacings between the drives. I've got one on order so i'll see how it fits.