Flying EI via LAX adds at least 2.5 hrs each way unfortunately - it's about as long as flying via CPH with all the joys of flying on disconnected tickets (no interline) through LAX.

ORD is an option I forgot, though I'm not much of a fan of AA's service (or of ORD itself, especially in the winter.) Now that NW is flying the 332 on SEA-AMS w/ ptv's and power ports in Y (good riddance to the DC-10!), AA is less appealling and more expensive.

Really, only LHR and AMS transfers get you there in under 14 hours (when everything's on time) on a single ticket - and only BA can get one there in 12. SAS was a more appealing option (despite the extra distance) when they had Connexion service on SEA-CPH, but now that that service has been shut down, they've been relegated.

SEA-DUB should be doable in 9.5 hours nonstop.