Then according to the rules, X gets to move anywhere. Pick another corner board, make a move in the NW corner, which forces them back to the NW board. Then their best option is to move in the same square of the board you just came from, since you won't be able to send them back to the NW board again. In that case, you move in the same corner as the board you are in, forcing their reply to the same board you're playing on.

This would be the general strategy, although I am now no longer sure you can force a win through. The options for moves for O starts to grow past what I can work through in Paint right now.

After that it's pretty easy to force a win. Whatever square they send you to, you just send them back to one of those two squares.

I challenge you to a game where you are X then. Because I can't figure out how you force a win like that.

I take it back. The key is to line up three master blocks with x's free move. Then the game is perfectly won by x.

I'm not entirely sure how to do it anymore, but playing with the perfect AI posted somewhere else in this threat convinces me it's impossible to win if you don't start first.