Well, in a sense, *all *Catholics can be relativists without being heterodox.
All moral relativism states is that we don’t know the truth. Certainly there are many, many questions which remain unanswered–and thus we are permitted to be "moral relativists’ in these areas.
Catholics can be moral relativists on torture, capital punishment, spanking, evolution, how many children to have, whether to abstain from fish on non-Lenten Fridays, Marian apparitions, whether praying the rosary is beneficial, receiving Communion in the hand or on the tongue, Latin Mass vs vernacular, vigil vs Sunday, etc etc etc…