By the look of the names of those scripts, i.e. "pppoe-init.in", they need to be compiled first.
As mentioned in the wiki, the trick to getting the required files into an extension is either to use DESTDIR or to otherwise copy the required files to a temporary location such as /tmp/pkg.
Once the files - for example /tmp/pkg/usr/local/bin/pppoe-init - are all copied to /tmp/pkg, squashfs-tools-4.x can be used to create and extension as follows: $ cd /tmp
$ sudo mksquashfs pkg/ extension_name.tcz
$ sudo chown tc:staff extension_name.tcz
If you cannot use DESTDIR, then something like this will work: $ touch mymarker
$ sudo make install
$ sudo find / -not -type 'd' -cnewer mymarker | grep -v "\/proc\/" | grep -v "^\/sys\/" | tee files
$ vi files [edit out unneeded files and save changes]
$ sudo tar -T files --numeric-owner -zcvf extension_name.tar.gz
$ sudo chown tc:staff extension_name.tar.gz
$ mv extension_name.tar.gz /tmp/pkg
$ cd /tmp/pkg
$ sudo tar xzf extension_name.tar.gz
$ rm extension_name.tar.gz
$ cd ..
$ sudo mksquashfs pkg/ extension_name.tcz
$ sudo chown tc:staff extension_name.tcz