Ouch!  Suggest you work with the mother so that she learns to position the
baby so that the crack is at the corner of the baby's mouth -- position of
least stress.  Clutch hold should do the trick.  Trick is not to continue any
stress on this damaged area and mom may not be able to position well enough
in across-the-chest positions at every single feed.

Have had some good success with persistent cracks with the radical change of
position plus trace of Bacitracin alternated with Lansinoh. Bacterial
infection can delay healing.  Breast shells for comfort between feeds also
helpful as nipple can remain extended vs flattened in bra.

Joanna Koch IBCLC in Los Altos, CA