We play some songs by some bands that tune flat - somewhere between E and Eb. Not even a whole step down. Retuning all the instruments just to practice along with the recording is a drag.
Fortunately, Apple ships a nice pitch shifting Audio Unit. I put all my songs on an iPod anyhow. To practice, I bring the iPod audio in on one of JambaLaya's channels, then choose 'Pitch' from the first Effect insert. Now play with the pitch slider. If you save the file, the state of the pitch shift effect also gets saved along with the song so you're always ready to practice without retuning.