Maybe its a bit late to answer but I did it on my megatronics board. use pin 46 (I forget the AUX number, you'll find it on the schematic) and you 'll need to define the servo pin in pins.h
something along the lines of : SERVO0_PIN 46
remember that the servo will use your usb port's +5V.
*ALSO*
If you have a LCD screen attached and a servo motor, I recommend that you remove the +5V_USB jumper because, you could have some trouble.
I forgot to remove mine and it blew up in my face (the megatronics board) :-(
Good luck
something along the lines of : SERVO0_PIN 46
remember that the servo will use your usb port's +5V.
*ALSO*
If you have a LCD screen attached and a servo motor, I recommend that you remove the +5V_USB jumper because, you could have some trouble.
I forgot to remove mine and it blew up in my face (the megatronics board) :-(
Good luck