I would wait it out. Give the fruit a week or more to do their thing. On the other hand, when I think of the flavor of blueberries I think of a very subtle flavor, and the flavor of a stout is very pronounced. If, after 10 days on the blueberries, you're still not getting the flavors you want from the blueberries then you might consider adding more puree. Yes, you can put the blueberry puree on top of the beer just try to not splash it around too much.
For a minute there I thought this post was going to be about muffins