PREHEAT oven to 350º F. Grease 2 baking sheets. Drain blueberries; set aside.
COMBINE muffin mix, flour, butter and eggs just until combined in large bowl. Fold in 1 1/2 cups morsels and drained blueberries with floured hands. Shape half of the dough into a 12-inch-long roll (dough may be sticky). Place on a prepared cookie sheet; flatten slightly until about 2 inches wide. Repeat with remaining dough.
BAKE for about 25 minutes or until a wooden toothpick inserted near the centers comes out clean. Cool on baking sheets on wire rack for 1 hour.
CUT each roll diagonally into 3/4-inch slices with serrated knife. Place slices, cut sides down, on ungreased baking sheets.
BAKE for 10 minutes. Turn slices over and bake 6 to 8 minutes more or until light brown (do not overbake). Transfer to wire racks and let cool.
PLACE remaining morsels in small, heavy-duty plastic bag. Microwave on HIGH (100%) power for 20 seconds, knead bag to mix. Microwave at additional 10- second intervals, kneading until smooth. Cut a small hole in corner of bag; squeeze to drizzle biscotti. Let stand until drizzle is set. Store in an airtight container at room temperature up to 24 hours or freeze up to 3 months for longer storage.