And most of all take care not to do anything that might appear like cloaking or you run the risk of getting bowled.
I presume Aer Lingus has you thinking about this
WRT letting
SE's see other versions of site, why not simply use internal linking and they will crawl the other versions? There's a good chance the
SE's will be able to figure out which content is most applicable.
Are you going to have multiple content on each URI or are you going to redirect to multiple URIs based on geotargeting (country in the query string or something similar)?