Mick,

If you installed Amplitube (which came with BIAB 2012 I think), There is a harmony stomp box that works with it. I don't think the harmonizer comes with the free version, but the Custom Shop sells all of the pieces of Amplitube gear separately. You could buy that one item for 5 or 10 bucks.

Several people here are using Amplitube in real time, so it should do what you want.