When any Paretroplus is not kept in a group, my experience has been they become either hyper dominant, or extremely paranoid.
As a group I kept mine with smaller Central Americans, although the centrals quickly out grew the kieneri.
I would suggest something with a totally different body shape than the kieneri, and as LS2012 suggested, something with a much milder temperament than many centrals.
Anything like a Parachromis, or Herichthys would probably kill kieneri
I have found some of the genus Astatheros to be less aggressive, or Archcentrus nanoluteus because it stays small (like kieneri), and has a totally contrasting color, despite its similar body style.
Another Madagascan that may be available where you are, is the genus Ptychochromis, this is arguably the Madagascan equivalent to Geophagines, or Thorichthys.
A nanoluteus

Astatheros rostratus

Ptychchromis sp tarantsy (these came from LS2012)

Pty sp east coast gold, pic from some years back.
