I've just won this in five games and here's how I did it..
You need to have the correct structure of the game board to allow all seven letters to be placed, meaning horizontally the row can only be taken up with one other letter. (See SneakyStabbalot's solution for info about the board - on the Win 8 version of this achievement)
I then typed the 7/8 letter that made up the combination for the possible row into this website and waited for one that would fit with the boardhttp://wordsolver.net/
I ended up using my seven letters to add onto another word so I ended up with my seven letters spelling REVISAL but the A adding onto the on board word WAY.
Any questions please comment and please don't downvote without saying why!