Read here:

http://line6.com/support/thread/69729

Not possible with a standard guitar over implemented effects, but possible with a JamesTyler Variax guitar.

Demo see here:

http://www.youtube.com/watch?v=qrKtyYX3k_c

But you can try this one, better than nothing:

fx 1: Preamp (from EQ category), change HPF about 350 - 500 Hz, because a sitar doesn't have bass sound.

fx 2: Pitch Glide (from category Pitch), change pitch to +12.0, Mix at about 50 - 60%. This will generate a mixed octaved sound.