I don't know the answer but maybe can point you in the general direction:
1. Does Irish withholding tax apply if the Irish company hasn't made a payment? My limited understanding is that if an Irish company pays for certain categories of sub-contractors, royalties or covenants then W/T is deducted at source. In this instance, the Irish company hasn't paid anything.
2. Do corporation tax 'group provisions' assist? If there's a 75% shareholding relationship between the parent/ subsidiary then certain 'administration relieving provisions' reduce the tax compliance burden (certainly for VAT, maybe for other intra-group transactions such as the one you're referring to).
3. Check out 'close company' rules re loans to participators- I think they probably are not relevant but it might be useful to verify it yourself.