You have to make her think she thought of it, sorta. It so far has worked for me.
eg:
I want to paint my car. I know the Mrs may so no.
"I was wondering dear, if you wanted the color changed what color would you like for my car..........oooo purple, that sounds excellent, might just do it that, might as well motor isn't in the car"
I want the interior done
"What do you reckon would look good on the inside of the car ??"
"purple, black and silver ...... "
"hmmm purple, black and silver ?? Yeah sounds alright dear, I might just do it, thanx"
I don't know how bout:
"Hmm some mags would look alright on this, what do you reckon............."
Then show them some mags of what you like, plus ones you don't and cross your fingers she doesn't like the ones YOU don't