I'm not a financial professional, but I would recommend you tell the Revenue exactly what you've said here (if asked). Have you any supporting correspondence to back you up?
Even if they didn't accept your explanation, the setup [i.e. the money being in an account in your name] looks at face value as though it was effectively an interest free loan (not gift) to you, which you repaid without making any profit, so possibly there wouldn't be income tax or CAT (gift tax) implications anyway??? [Not sure about this.]
Were all the withdrawals simply money sent directly sent to him (which would make it fairly simple), or were they used to buy stuff from a 3rd party for him?