This is the way.
The resistor is in series with between the negative terminal and the power supply and you are measuring across the resistor (in parallel) with the DAQ module.
The only question is if the resistor needs to be 470 Ohms (best from the respect of resolution bit count wise) or 330 or 270 Ohms lower compliance voltage. Hopefully the 20 mA value is something that you can easily obtain by running the system at 1 Atm or something so that you can check for full scale.
