first off, you're too early for "summer" 2015. tickets are now available for june 20 at the latest.
there's no secret, you just have to keep checking every day. it appears anecdotally that award tickets appear after midnight UK time so around 4 pm here on the left coast.
we have just booked 241 CW seats from YVR-LHR-ORY for the end of may. since we want to stay around 5 weeks, we'll look for end of june returns when they become available as of around the 7th of july and we'll call in to add them to our 241. of course we'll have to pay a change fee.
remember it's 355 (one year minus ten days) days out only so if you've been looking, you're probably too early.
i have seen tons of CW and F availability in july/august 2014 at the end of last year.
patience and persistence is the name of the game.