I have seen where some use a servo for each nozzle mounted to the side of the extruder with a piece of a soda can bent like an L. When the extruder being used gets used it moves the tin away from the nozzle. When it is not in use the servo moves the piece of tin to block the unused nozzle. I went looking through thingiverse for you and did not find anything along these lines specific to your BIBO so you might have to get creative and make something yourself. Here is someone's design for this function on a different dual extruder printer. Look closely at all the pictures and get busy with the rapid prototyping: https://www.thingiverse.com/thing:2777682 I actually think the design in the link I sent you has the tin hard mounted and it moves the nozzle to and away from the tin for printing. A little different but the same.