Look at this recipe and see if it may be something you'd like to use 
http://www.justberryrecipes.com/ber-0038947.html
Are you using fresh berries or frozen ones? I guess you could use either with this recipe. I've made it with huckleberries, which are close to blueberries, when they are in season around here and I get rave reviews.
It's not really a recipe but whipped cream, sugar (to taste - maybe a couple of tablespoons) and then mashed berries. It makes like a mousse for a filling. You really could use any berry. I liked this recipe because it's not as sweet as some jams, the frosting seems to cover the needed sweet factor 
. I've made this with white cake and white buttercream and everyone asked for seconds.
Hope this helps.
Kate
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