How to have double extruder and double Z motor on a 5-driver board? We are using the Board SKR 1.3 with the following pins:

/**
 * Trinamic Stallguard pins
 */
#define X_DIAG_PIN           P1_29   // X-
#define Y_DIAG_PIN           P1_27   // Y-
#define Z_DIAG_PIN           P1_25   // Z-
#define E0_DIAG_PIN          P1_28   // X+
#define E1_DIAG_PIN          P1_26   // Y+


We need a double Z motor, so We have defined the number of stepper drivers to 2 and it works like a charm:

#define NUM_Z_STEPPER_DRIVERS 2


Here is the problem, We need to have a single extruder with two heating zones, not a real second extruder. We have defined the number of extruders to 2:

#define EXTRUDERS 2


We want to reinforce that the second extruder does not exist, we only need the second heating zone. It's a big hotend with two different heating cartridges, that is, two different temperatures. So we do not need the stepper driver, only the temperature.
Then we get the following error messages:



We have thought of enabling the chamber and use it's pin, but we got stuck with all the structure for it:

#define TEMP_SENSOR_CHAMBER 5


#define CHAMBER_MAXTEMP  250  // Extruder first temperature zone


#define HEATER_CHAMBER_PIN 24
I second the previous answer if running second Z motor in parallel, just split wires or buy adapter consisting of two females to one male, Z motor on most printers don't draw huge current (or at least in smaller less frequent intervals to give things time to cool). 

Erm I extruder with two temperature zones, hmmm buy a larger heating element, like a E3D Volcano or I believe they have an extreme version now, mine is rated for 40&nbsp;W+.

Or you could use external MOSFET with separate Arduino PID.