Got idea of making a modular expandable Multi-Colour Jig Bracket/Joint here by utilizing the existing screw holes. Can be expanded to how ever you want it to be.

This bracket are meant to be used for this http://www.thingiverse.com/thing:2111918

Designing a single jig with more than 2 inputs is not easy since we got to watch out for overhangs inside there that is unreachable while we had to maintain smooth passage for the filament to go through these jigs. Although it is kind of bulky, big and takes a lot of space, but this jig is flexible, can be switched to any extruder number you want.

Do NOTE that you need to retract even more on each stack and do help to test them out.

https://youtu.be/qlx8FXCOUnw