I tried this, but that´s not the issue.
I´m using Dam Small Linux, they somehow make links to core utils, which are inside
a compressed file (in fact the whole linux stuff is in one compressed file).
Some of it will be uncompressed onto a ram disk, which is write protected,
but the whole /sbin seems to remain inside the compressed file and a particular program
is only extracted somehow and temporarily, when the command is beeing called from the command line.
When I´m trying to copy my binary into the directory /sbin I get a 'write protected' message, even as su, which is logical.
And since I´m unable to re-create the compressed file including my executable, I´m looking for a workaround.