I just now booked SFO-DUB for $499 all in for 6-10 November. Not as good as my $300 SFO-FRA trips from earlier this year, but still cheap enough for a *A routing to a place that I actually want to visit!

Routing is SFO-IAD-LHR-DUB-LHR-SFO. SFO-IAD is on UA, LHR-DUB-LHR is on bmi, and IAD-LHR and LHR-SFO are bmi codeshares on UA metal.

I used multi-city and entered 4 segments (SFO-LHR, LHR-DUB, DUB-LHR, LHR-SFO). Not all dates I tried worked out to be cheaper, but the prior weekend priced out the same.

NB: You won't always see the "Congratulations/lower fare" message to indicate that the trick worked. I might have missed a few options until I realized that I needed to scroll down to the bottom of the page to see if the price changed.