I thought LGW-JFK was going to be on the 744. Or did I dream it. Anyway, unless they are going to operate LGW-JFK on the A318/9, I don't see how they can do a W pattern, unless you mean back to back LCY-JFK, where the crew will nightstop at LCY.
As for nightstopping at SNN, I am not sure how that is going to be feasible, considering that they are only going to be stopping on the outbound flight only, unless that is going to change. In which case they could make you operate SNN-JFK as a shuttle.
I'm off sick and bored, so let's see what they could do with this route:
Day One: Position LGW-LCY, operate LCY-SNN
Day Two: Operate SNN-JFK-SNN
Day Three: Operate SNN-LCY-SNN
Day Four: Operate SNN-LCY, Position LCY-LGW
Ok, I officially have too much time on my hands but you get my point.