Have you considered either a transfer at the airport to a flight to Tralee or using the train? Flight lands in at 11:50, all going well there is a bus from T2 at 12:10 which would mean you could catch the 13:00 to Cork, changing at Mallow for Tralee. Could sell it as a sightseeing way to cross Ireland. It is doable, it would be the additional cost and travel that would have to be accounted for. Flights back to Geneva are at idiot o'clock in the morning though from Dublin so they would have to be travelling back to Dublin the night before (night out in Dublin to finish their trip?)