Help, please - how to put a build on an USB stick so that it will boot on an XO ?

[Mikus Grinbergs]

I do not have a Fedora system.  I've been using 'livecd-iso-to-disk' 
script for building USB sticks from .iso files.  But that never has 
worked for me with XO-1.5 builds.  And just now it failed with a 
recent XO-1 build.  [Booting stalls - can't mount root filesystem.]

A while ago I read a complicated procedure to build an USB stick 
from a tree.tar.lzma file -- now I can't find that description.

Please - how do I build a bootable USB stick, for example from the 
os40_build files ?   [Preferably using just an XO-1 for this.]

Thanks,  mikus