I don't know, of course, if you've ever seen "ashes" left from a human cremation, but they are quite coarse, being only the leavings from the bones, unlike the fine ashes left in the fireplace from wood fires. Therefore, a consideration would be that they don't incorporate into the soil very well and would still be quite visible months, if not years after the "scattering". This may not be unsettling to you, but a friend (here in the U.S.) that tried the "rosebush" solution was less than satisfied.
Actually, the ashes wouldn't provide much in the way of fertilization either, since, again, they don't have the concentrated ph of wood ashes...