AD5421 in 3-wire circuit

I have an existing circuit using the AD5421 as a 2-wire loop-powered transmitter.  It has a CPU, LCD display, sensor ADC, and an AD5700 for Hart transmission.  Works great.

My customer wants to add additional circuitry that would only be used if the device was connected in a 3-wire configuration, since it would draw too much current for loop power.  So the device would be able to operate as either a loop-powered (2-wire) device or as an externally powered 3-wire device with additional capabilities. 

Can I accomplish this with the AD5421? 

If so, what do I need to change? 

If not, is there another part that I can use?