Bonnie
Try these I think they should help you.

Blueberry Pierogi Filling
Wash, drain, and drip dry 1 pt. blueberries. Some cooks sprinkle the blueberries with sugar before filling pierogi, but that makes the filling quite runny. We feel it is better to fill them with just the blueberries and then sprinkle the cooked pierogi with powered or granulated sugar on serving platter. This is a great summertime favorite, the more so that the small wild blueberries found in Poland's forests are far tastier than the commercially grown variety available in America. Note: Your blueberry pierogi will be less runny if you sprinkle the berries with 1-2 T. flour or potato starch.

Cherry Pierogi Filling
Remove stems, wash and pit 1 lb. or so sweet or sour cherries. Place in colander and gently press out some of the juice, taking care not to damage fruit. Fill pierogi with 3-6 cherries each, depending on the size of your dough rounds. Sprinkling cherries with flour or potato starch will help take up some of the juice and make your pierogi less runny. Variation: If fresh fruit is not available, canned cherry-pie filling or cherry preserves containing whole cherries may be used instead. Place 2 c. pie filling or preserves (or 1 cup of each) in a pot and heat to just below boiling. Drain and sieve, and when dripping stops, use the fruit to fill pierogi.

Prune Pierogi Filling
Soak 2 c. or so prunes overnight in water to cover. Add 1-2 sugar and 1 T. lemon juice. Cook on low heat until tender. Remove pits, place prunes in sieve, and press out excess moisture, then fill pierogi.