Playing without Giving away your Strategy

Perhaps you are about to play a series of three games of cram against an opponent in the final round of a cram tournament. Your scored better than your opponent in the tournament thus far and must play first in the first and third games. The winner of the tournament will be the player that wins 2 of those 3 games.

While playing the first game, you can see that you are losing, but suddenly realize there is an really good strategy for winning from the start as long as you go second. Since this tournament uses initial 8 x 8 boards, you can use a symmetry strategy to mimic the other player's moves! Great! The next game is yours!

Unfortunately, you also realize the strategy is easy to follow. As soon as you use it against your opponent, they will be able to implement it themselves in the final game and win.

Is there a way to implement the symmetric-play strategy but disguise it at all? In general, is there a way to mask the fact that you are using a simple strategy to win?

In Nim, it is difficult to follow someone making the correct moves if you do not know how to evaluate the game boards. If it was plainly obvious what the other player was doing (perhaps XOR is your favorite math operator) then perhaps you would pick up on it quickly.

I tried this once, keeping a "turn behind" in the symmetric-play strategy. I kept making the play my opponent had made two turns ago, whenver possible. As I recall, it got messed up and I had to ditch it part way through. Is there any good way to keep this going? I feel this would be more difficult for an opponent to follow... if it works!