I would cut both the letters and the big baby head in vinyl, and use those a paintmask. Place the masks on the stock. Handpaint the area white and place the laser printed decal of the head on top of this. I provides the white background and will give and illusion of it being hand painted.
With the white big baby done in vinyl, I've got a white vinyl mask for the clear laser sticker, but is there any reason why I couldn't just use a white laser label for big baby's face? I've got some and it would save me ordering and waiting on clear labels?