I believe it should be arranged via your handling agent. We've used Westair, give them a call on +353 61 475166 and check if they can help you.
Not sure if its been mentioned before but remember that there's a list of airports that can be used as first point of entry. No other airports are approved as they lack the facilities to take care of waste from inbound flights....or so I have been told...
Good luck!
CP