RAMPS dual extruder and PWM fan control

As shipped it seems as if the ramps board can either support 1 extruder and 1 fan, or two extruders. What would be the easiest way to have dual extruders and yet still have at least 1 fan under gcode control?

My thought was to use the motherboard 34 standard config for the two hot ends, and then use one of the available PWM outputs from the arduino together with a small MOSFET circuit many of which can be found on thingiverse. To get the g code control, I'd probably hack the firmware to apply the M106/107 commands to my new pin instead of two the standard fan pin.

am I missing anything with this?

The easyest way would be to do as you say. The following circuit works well [www.thingiverse.com] and you just need to set which pin you want to use in pins.h no hacking required

Yes - that's the circuit I was looking at - nice and compact.

BTW, I was using the term hacking loosely. I figured it would be something easily modifiable in pins.h.

Thanks for confirming everything for me.