Yeah I'm still roaming around sometimes like an old ghost.
Well... These days I'm not "constructing" that much, I'm more into unity, and I've became proficient enough to feel quite limited when I try something on construct :D...
That being said, if I remember correctly and after having reread a bit of the plugin, I'm actually drawing the polygon in a 2D (non webgl) canvas and then using the resulting texture on a WebGL quad.
And according to that StackOverflow answer
there's nothing to control the aliasing, you'd have to write things pixels by pixels using some aliasing algorithms (I used one once for grid based line of sight...)
So well... you'd have to either tweak the plugin to just do that, or find a way to draw polygons directly with gl calls (probably sending the vertices composing the polygon on the gpu directly, and since it only accepts triangles, as far as I remember, you would also need a triangulation algorithm... there's one in the box2D/physics plugin I think, for collisions... but yeah it would be a lot of work and I don't remember what C2 is exposing to help you on that... And that's why I choosed the easy road)
And even with that, I'm not sure where C2 activate or deactivate antialiasing for WebGL if it ever does it (I think it does when you choose point sampling... yeah long time no C2 :D)
So yeah, no easy answer on that one, sorry...