Installation on a USB stick is quite easy. I just have done it myself.
Forget my post above (number 2 in this thread).
Follow the installation as described in chapter 1.3 of the Lubuntu manual and select the correct storage device at this step:
Important: Double-check that it’s the USB stick you’ve chosen!
Mark ‘Erase disk’ as depicted and go on. That’s all.
(The picture is taken from the Lubuntu manual.)