What about:
cat > $RPM_BUILD_ROOT%{_menudir}/%{name} << EOF
?package(%{name}):\
command="gogglesmm" \
needs="x11" \
section="Sound" \
title="Goggles Music Manager" \
icon="gogglesmm.png" \
longtitle="Goggles Music Manager"
EOF=> that's the way I do it (when I do it, not so often

); I do not understand the content very well, but....
But I'd think that with the .desktop file correctly placed, it should automatically appear

(and that's not happening

)