I have solved the problem by modifying my route. New plan is to go "Open-Jaw" with Turkish Airlines and the route will be the following: HEL-IST-SIN and HKG-IST-HEL. This gives me 13057miles and im planning to cover the rest 1159miles by adding oneway SIN-MNL with Singapore Airlines. Y-class gives full 100% of miles which in this case means 1447miles. Problem solved!