Simultaneous dual too?

I have seen a few pictures of dual extruders both running at the same time, but how is it done?
I do not think it can be selected like that in slic3r. I thought about making a Y-cable for the stepper motor as one possibility.

The main reason I want to do it is to easily calibrate the exact extruder offset in X and Y, but there are other high production possibilities.

Any ideas? maybe a certain G-code, or a find and replace in the G-code?

If you do run a Y-cable for the extruder stepper, you might need to bump the digipot in the firmware to accommodate the extra load. Or just tune your pololu up a bit, if you are running ramps.