Original code from http://www.thingiverse.com/thing:24195 before I applied fixes to it.
Original attribution by Joe Cabana is:

Both Extruders At Once For Replicator by JoeyC is licensed under the Creative Commons - Attribution - Non-Commercial license.
Fixes to make it work with MakerWare 2.4.1.35 which outputs A or B feed values rather than E feed differences for a single extrusion during the G1 command.
I was able to DualExtrude Emmet's mini-gears with this script.