Currently, there is no method of combining an external filament to what is installed in the AMS.
Add color 0 (or whatever else is available) so you can paint your object any of the four filaments in the AMS plus one for the external spool in the back (on X1C)
The purpose is to alternate PLA builds with PLA-CF for certain layers, or PETG + TPU for certain layers.
This will require modifying the Gcode to make it stop printing when the external filament is required, cut the filament at the head and retract it and wait on the user to switch. Once the external filament printing is done, the user will have to manually retract the filament and restart the AMS, or have a Bowden combiner so the AMS can feed the next color filament down to the extruder.