You can’t - easily.
You can, if you edit the sketch in the “emon” front end of the emonPi and send the currents - they are measured and calculated, just not sent. But if you do that (tortuous in itself), you must remember only ever to update your emonPi as an emonBase, never as an emonPi, else your carefully edited and uploaded sketch will be erased and returned to the default. Don’t ask me why it has to be like that, it must have seemed a good idea at the time.
This might help - if it is still accurate. If it doesn’t seem to make sense, ask again.
And when you’ve done that, you need to edit emonhub.conf to tell it about the new variables.