Carefully peel back corn husks to within 1 in. of bottoms; remove silk. Rewrap corn in husks; secure with kitchen string. Place in a stockpot; cover with cold water. Soak 20 minutes; drain., Grill corn, covered, over medium heat about 20 minutes or until tender, turning often. Cut string and peel back husks. Cool slightly. Cut corn from cobs; transfer to a large bowl., In a small bowl, whisk the oil, vinegar, chives, salt and pepper. Pour over corn; toss to coat. Gently fold in blueberries and feta. Garnish with additional chives as desired.