matriax, the minimum size is a 'feature' of the r2.3.0 Box2D library I used - there is nothing directly that I can do to affect it.
What I can do is provide you with a method of changing the default world scale. It is currently a hidden value (0.02 - same as for standard Physics). If it is changed to 0.1 then the plugin will support 1 pixel tilemaps (I just tested it and it works ok). If the number is set too high then the plugin library's collisions become visible (objects that should be at rest appear to jostle and move around). Of course, the world gravity will have to be changed as well. Would this suit your needs - it'll take me a few minutes to add a method to do this and then upload?
Edit - I will create another draw example (the one in the demo broke because of changes to the plugin).