It is now possible to find a flight from KUO - IST now as TK has now filed a fare which allows transferring from AY to TK for this market. If I found it out earlier, I won't have those hassle avoiding the expensive single-journey KUO - HEL flight on my previous trip because that KUO - HEL flight was the best flight for my timing which I could reach by bus.
My hassle was that, I was taking the HEL - IST flight at noon, the 09:15 KUO - HEL one-way was too expensive and no award availability, and the 07:00 flight with award availability was too early from Nilsiä where I was staying because bus 61 didn't run so early in the morning. And for train travel to HEL, the train from Siilinjärvi departed at 05:11 which was also too early for any public transport from Nilsiä, and I couldn't get anyone to drive me at that time to the train station also.
The result was to get someone drive me a really long distance from Nilsiä to Kuopio and get a night of hostel stay there. If the KUO - IST fare was available then before I book the HEL - IST - HKG, all these hassle could be avoided as my intent was to KUO - HEL (transfer) - IST (stopover) - HKG.