ty
and i just confirmed that this was true:
"i think you need to swing really far from the shop in the air, so that when you hit the water, it is in the wilderness and not port town, and in F2 it should keep your location as "shop"..."
I tried it a few mins ago and it worked. I cant be hurt by other players, or use spells, its just the same restrictions as being in the shop (you cant hurt other people either). As soon as i enter an area like port town or the woods, then invincibilty will switch off
EDIT: also, when you eventually die your body cant be picked up.