You might make a big deal about how much you support someone else's plan while secretly wondering if it's really a good idea or not. You could give yourself away if you are overly effusive and others will see through your facade. Remember, it's more important to be sensible in your approach than to bring unnecessary attention to the situation.
I just read this a few minutes ago. Earlier a situation presented itself in which I could have fallen into this trap. Luckily, I told the person I support them, and understand what they have to do, but made clear that I do not necessarily agree with the plan, but I do accept it as reality. So, I think that's pretty sensible. I beat the horoscope to the punch this time. Yay me.