Would the easiest way to solve the problem not be to discount the scores of the games against the team who gave the walkover. That way this particular group would have finished as follows:
Wanderers - Points scored 53
- Points diff 26
Ballymun - Points scored 52
Man O War - Points scored 25
Therefore with those scores discounted Wanderers would finish top with Ballymun 2nd as per the table. Granted it may not be the fairest way to treat it but it nullifies the score in the game that Man O War couldn’t score in and prevents the county board having to attempt to schedule in a playoff.