My elite plus status is expiring at the end of May, and so were my 2 vouchers. However, I was successful in upgrading my flights from AMS to CANCUN and back - for vouchers. Not a bad deal for 550euros.
Called the TK 1800 number, and asked to check whether there is upgrade (J) availability for the flight I was looking for. Ofcourse, it wasnt possible - due to november changes... etc etc.
I booked a ticket on expedia.com with a 24 hour free cancellation, and then called the TK 1800 number again. I gave my eticket number and the agent was able to process the upgrades for all the segments with 2 vouchers, in less than 10 minutes. Fantastic! Cant wait to try to new 787 on this route in September.