Kempis can find out for sure, but I have a feeling that on the CPH-SEA route, the 767 used is generally the 2 cabin version. It's the 3 cabin version that you need. Then, if they run the middle cabin as economy class, your *Gold status should help you get seated there.

Sorry, but as with many FF schemes, SAS and EuroBonus only allow upgrades for their own members (and their families). And even then it's a standby gate upgrade (officially) although upgrades at check-in using the certificates are sometimes done.