For a spreader load in a .410, using the simple method of a card wad separator may be the easiest to produce. I suggest starting with but one in the middle of the shot column and going to the pattern board to see & judge the effect.

BTW, You can make an arch punch by champhering the edge of a suitable dia tube and punching the card wads from shirt boards or any suitable card stock, inclusive of index cards. Chosen card material & thickness will likely affect dif results.