Another solution is to run KiCommand, but it requires the nightly version at this point.
Works with nightly
WARNING: The nightly version is not guaranteed to produce files that can be opened in the stable version. There is not even a guarantee that one nightly build can open the files produced by another nightly build. (In most cases there is no problem but you might encounter one. Just know the dangers that come with using a development build.)
It can create regular polygons with as many edges as you want to draw. Then you can use the ‘regular’ command to make it a regular polygon (equal edges, equal angles). At this point, it’s only on drawable layers, not copper, yet. But you can get the points you need from the file after saving. Then maybe change it to a copper track afterwards.
Use ‘regular’ then delete the segments you don’t want. I find 32-64 segments is close to a circle.
Future commands will make creating copper nets possible directly.