Quote from the Numpty Physics homepage:
If you wish to be clever, edit the level file directly – it’s just a simple text format.
As I wished “to be clever”, I did:
Interestingly, it is not possible to create perfect sqares. It is possible to draw “horizontal” lines, but as soon as you try to create vertical ones within a square, weird things happen. This is why the vertical edges of the squares seen above are not perfectly perpendicular to the baselines.