This may well have been pointed out in these forums before, not sure.....
In trying to work out an alternative to using the expression pedal to control the pitch parameter on the Pitch Glide on my Pod HD500, for the song Lonely Boy by Black Keys, I stumbled on this.
You can set the pitch parameter to be controlled by the variax tone (or volume) control, and with Min set at 25% and Max set at 50%, you have a very usable tremelo. With JTV you can lock the tone or volume control per patch, but even on non JTV this effect is very usable with little tone drop, when you don't need to do big dive bomb tremelo usage. Great for soloing Jimi Hendrix style, etc....
As it turned out, I stuck with the expression pedal for that song, but I'm glad I stumbled upon this for other uses - sometimes my real tremelo chucks it out of tune if I go too crazy mid song... :rolleyes: