As requested by Volvo2002, here is a miniguide of how to remove the gearknob. This is for a Phase 2 S40. Older gearknobs differ and the procedure is different.
Hope this miniguide helps a few people.
So here we go:
First of all, lift up and remove the rubber MAT
Unclip these 2 clips (by pushing both of them inwards) and lift the plastic base
You will need to gently unclip the four clips pointed by the yellow arrows. The lower two bits pointed by the green arrow are not clips, but just holding the lot together. A lot of people have broken some of this clips by trying to unclip it from that end.
You need to push in this clip as well as the one on the other side at the same time and gently push down the gaiter and the its plastic ring. I used by leatherman to press the lower part of these clips. Any large pliers will do too
Close up of the clips. You need to push the lower bit, as the top part needs to be releases
Push the gaiter with the plastic ring downwards (yellow arrow) and then use a flat blade screwdriver to lift the clip pointed by the green arrow. There is one more clip on the other side, so you will need to use another screwdriver. While lifting both clips a tiny bit outwards, just lift the gearknob
and you are done
Close up of the gearknob and the gearknob stick