Calculating energy between a single cation and the rest of the system?

GROMACS version: 2018.3
GROMACS modification: No

So I have a system consisting of cations, anions, water and protein,
What I’m trying to do is find the Coulomb’s interaction energy between Each cation and the rest of the system.

In that regard,
Is there a more convenient way of doing it without creating index groups for every cation and rest of the system minus the said ion, and then running an mdrun -rerun for each pair of [cation] and [system without that cation] energy groups ?