If you find a SAS ticket in W (most expensive 25% class) or lower, but not V (cheapest 100% class long-haul), on wideroe.no, you can book it, and then use the chat-function to rebook it in V without a service fee, just paying the fare difference. I have done it immediately after booking (starting the chat to ask if it's possible even before confirming the booking), but maybe you have 24 hours, since the ticket can be cancelled during that time? Only drawback for Swedes is that Wideroe will charge you in NOK, so you probably have to pay a couple of % extra with a non-NOK creditcard.