Hi,
Voltmeter as ammeter uses a shunt resistor to sense the current and measure the voltage drop across the resistor, as in a difference amplifier, if that's what you mean by "in series", 4-wire sensing.
If the second has an independent power supply (not powered by same red and black cables in photo for measuring), then you should/could be able to use a shunt resistor to measure current, you need to find datasheet information about the device inner workings and to know the possible input range, and calculate an appropriate value shunt resistor based on this information.
I don't know, but suspect that as the first uses the Black cable as voltmeter power supply negative/return and as the measurement negative, it might not be possible to place the leads at either end of a shunt resistor, but don't take my word for it. Again, you need to find datasheet information about the device inner workings and to know the possible input range.
Without knowing more about how those voltmeters are made, it's hard to say.