It can indeed be done without removing the dash. Quite rough, but it can be done.
Haynes manual will be handy for removing glovebox etc.
1. Remove glovebox as much as possible (Lid, top etc).
2. Pop end cap off the dash and remove the three bolts behind there
3. Remove pollen filter cover etc
4. Would be advised to remove the headunit and undo the bolts holding the facia on there too, but I never bothered. Would make life easier though.
5. The rough bit. Grab the bottom of the glovebox moulding and pull it forward enough to give some space to work. Then bend the support member forward. Doesn't need much space.
6. Remove the torx screws holding the motor on. These can be a bit fiddly.
7. Remove all plugs etc attached to the motor and drop it out.
Refitting is reversal of removal. Just bend the dash back into place.
No visible damage, no rattles, everything works as it should and now I have working heaters!