I have seen a report (but I can't remember where)
where a newly ringbarked tree was saved by transplanting strips of bark from
near the ringbark into the ring.
This was done by taking several strips of live
bark - of about 75mm to 100mm wide and of the height of the ringbark, from
different positions on the tree close to the ring and located so to ensure that
your new scars won't seriously disrupt the sap flow to the top of the
tree. Then trim the height of the peices to firmly fit them in the
ringbark wound and bind with a tape around the tree. I can't remember if
the transplanted peices were treated with anything before they were placed into
Perhaps an enquiry to field naturalist groups might
provide some more ideas.