And now, the day after, I find M availability for SK855-SK4741! on the LH webpage. Strangely enough, I only find availability on the Norwegian site, not on the Swedish one... Depending on when and how you need to return, you can get ARN-xOSL-BRU (M) and ARN-BRU (T) for as little(?) as NOK 2619.

One-way also available from www.sas.se for SEK 2176 in Economy (BK:?), all inclusive.