Do they not have three aircraft overnighting there anyway?
If you use 2 or 3 London-based aircraft to serve existing UK-Ireland routes, you save on keeping crews in hotels and as these would be new aircraft, you could free up capacity for new routes from the Cork and Dublin based aircraft.
Talking of which, what is the situation with establishing a pilot base in Cork. Even if they've negotiated a good rate with local hotels, it must be costing 400K+ p.a. to pay for the hotels, transfers etc.