Thanks for the replies - the plan is to book two one way redepmptions, to Hawaii via Tokyo with a couple of days in Tokyo as a stopover, then Hawaii to Belfast via LAX or SFO (with another stopover !)

Flying out from DUB looks like it throws up a few interesting routes, via Frankfurt (LH) or Copenhagen (SAS)

Coming back via the US seems more problematic - doesnt seem to be much business availability but maybe when Continental join star alliance that might change (and I can fly back t straight to Belfast).