Here's one way to do it. Assuming that you can put a resistor between the heater and ground, that is.
This is along the lines I was thinking, except instead having just the heater monitored, which looks to be impractical with this package, connect pin 4 and GND of the 8663 package between VCC and R1 of this circuit.
Bear in mind, the unit he referred to is 12V not 5V, but this is a good way to ensure the voltage drop across the current sense resistor stays well within the required 5% of 12V VCC.