Comment 10 for bug 1330252

This workaround passed along to me by Vagrant Cascadian works:

Write a script, say /usr/local/bin/lubuntu-custom:

  #!/bin/sh
  exec /usr/bin/lxsession -s Lubuntu -e LXDE

(For others less experienced like me, remember to make the script executable.)

Also write a corresponding /usr/share/xsessions/Lubuntu-Custom.desktop file:

  [Desktop Entry]
  Name=Lubuntu-custom
  Comment=LXDE - Lightweight X11 desktop environment
  Exec=/usr/local/bin/lubuntu-custom

(Alternatively, one could instead edit /usr/share/xsessions/Lubuntu.desktop to use that Exec command.)

And then set the default session in lts.conf:

  LDM_SESSION=Lubuntu-custom

However, my observation concerning this last step is that LDM does not default to this session selection. Rather it defaults to the last-used/selected session.