Just had a quick sprint through this thread without looking at all the details and it seems to have drifted off course somewhere on the way down here.
Is it not possible to draw the shape you need using the filled zone tool where the first click on the board pops up a window asking which net to connect it to?
Edit : forgot this bit again, I am using a new version
Version: no-vcs-found-fe62760~61~ubuntu17.10.1, release build
libcurl/7.55.1 OpenSSL/1.0.2g zlib/1.2.11 libidn2/2.0.2 libpsl/0.18.0 (+libidn2/2.0.2) librtmp/2.3
Platform: Linux 4.13.0-32-generic x86_64, 64 bit, Little endian, wxGTK
wxWidgets: 3.0.3 (wchar_t,wx containers,compatible with 2.8) GTK+ 2.24
Compiler: GCC 7.2.0 with C++ ABI 1011