Voltage bias for a single node simulation

I am running a simulation with a single node present (one sphere immersed in plasma) and I am looking to bias this node to a constant potential for the duration of the simulation. I see that the circuit editor allows for a voltage to be set between two nodes, but would like to know if there is a way to bias a single node to a set voltage with respect to the plasma potential. The goal is to investigate currents collected by this node while it is held at this potential (V) bias.
Thank you!

use the groundedPotFlag parameter (See SPIS v6.1 user manual, section 3.5.1)