Just had a look at my fruit book about bark ringing..
it's been done by taking 1/2" strip off.. :-X
Anyway..it says.."bind some insulating tape around the wound to stop it drying out and to assist healing. Seal the wound completely but do not poke the tape in so that it adheres to the cut surface. Remove it when scar tissue begins to form."
If yours is larger area, perharps you could use some plastic wrap around the trunk and tie it with string on both sides of the wound.