If one spouse seems to be taking the lead, I will ask if the other person has some interest or ideas that need to be considered while we are developing the design/proposal. Usually that gets me a useful answer and then I proceed appropriately. If I feel that one spouse is trying to use that ploy I will offer to help out with the explanations by being present to answer any questions directly so that "you don't get put on the spot about the details or any technical aspects that might arise". Usually they will accept my gracious offer to help them explain it to the absent spouse.
Especially since I won't normally leave a drawing behind.