Posts thumbnail grid with empty boxes/spaces

Hi, I am searching for a special kind of posts thumbnail generator.
There are so many posts thumbs generator but I would like to have a plugin where I can define precisely some empty spaces.

For example let say I have a grid of 5 cols and 10 rows.
I want to define easily box 1×1 is empty, and box 2×3, 4×4…

I would like to be able to define those not in the code but in the plugin interface so a normal user could update the grid alone.

Thanks in advance.
Miguel