Cornflower will thicken and reduce the sweetness. It's the basis of English custard which is popular with many desserts for exactly this reason. Make a thin paste in cold water and mix into the fruit shortly before the end of cooking, allowing it to cook.
I've also seen sultanas added to soak up liquid, ten minutes before the end of cooking, and I suspect if it's really sloppy you might even get away with adding white breadcrumbs.