(see here a related thing: http://www.thingiverse.com/thing:1200876 )

This customizable add-on funnel improves the interface between the Flashforge extruder and the filament guide tubes, and helps keeping the guides in place, especially for the filament that is not currently in use.

I printed it with ABS and glued with Tamiya cement for ABS. Before you glue, make sure to clean the hole of the printed part such that the tube fits nicely (it must go through the funnel into the existing hole at the top of the extruder). Also, make sure your align it accurately with the extruder hole.

The openscad source file is included so you can tweak the dimensions if needed.