You don't really need the extra step of "touch"ing the file - just *create* it using your favorite text editor and type the lxsession command into it, or directly by echoing the desired command string to an empty file using

echo 'lxsession -s Lubuntu -e LXDE' > ~/.xsession
or alternatively

cat > ~/.xsession
lxsession -s Lubuntu -e LXDE
and then hitting Ctrl-d to quit