Advise the enemy into doing things; introduce yourself as his best friend, his advisor, show him how he can defeat this one and that one, what he should buy and direct his actions against your enemies.

Present yourself as a trusted ally. Perhaps he will believe you and be hesitant about backstabbing you. You will profit from it.

You should really learn how to point with the finger on someone, telling everyone at the table how powerful he is and how he will win soon. Here you can exaggerate as you want, paint a horror image of total domination simply because he could theoretically do this or that.

If you can see that there is no chance to win anymore, use the time left to build yourself up a reputation. Choose one person you can influence and guide him to victory while punishing every backstabbing directed at you at any cost - they shall "learn" you always keep your word and your counsel is truth - they won't readily recognize that it won't be the case next time.