In response to your post (34), gitto, I was not proposing to draw an outline of the blanked-out cells but rather of the symbol within the blanked out cells.
The preamble says '...drawing a large symbol within the 78 resulting blank cells'. This is ambiguous: is 78 merely making it clear to the solver how many cells are to be left blank OR is it also indicating that the symbol is to be drawn in (at least part of ) ALL 78 blank cells?