Check with Leon, but I am pretty sure all you would have to do is some math to figure out what resistance you would need to convert the amperage signal to a voltage. For example to convert the signal from 0-100mA to 0-5 volt you would put a 50 ohm resistor across the circuit in parallel. You would then sample the voltage drop across the resistor with the 0-5 volt input on the plc. This is making the assumption that I did my math right and the amperage you are measuring is in a current loop which should compensate for the load applied to the circuit to read it. Again, check with Leon, but I think this will work.
Ken