How to install Windows 8 with BootCamp 5 Assistant via USB? I was able to put Windows 8 setup files on my usb from the installer. Now I just upgraded my machine to Mountain Lion. I have gone through the BC Assistant and it only asks for my Windows CD to be put into my drive. There is no longer an option to install via other media. 

Anyone know of a workaround to install with USB stick?
This doesn't exactly answer your question but may help solve your problem: create a bootable Windows DVD from the Windows 8 setup files, as explained  here.

I did it myself some months ago when upgrading Windows XP to Windows 8, and it worked without a hitch.

You will need:


Access to a Windows computer.
oscdimg.exe, a command-line tool for creating bootable Windows ISO files. This file is part of a larger download:


For Windows XP SP2 with KB926044/2003 SP1 with KB926044/2003 SP2 you'll need the Automated Installation Kit at http://www.microsoft.com/en-us/download/details.aspx?id=10333
For Windows 8/7/2012/2008 R2/Vista/2008 you'll need the Assessment and Deployment Kit at http://www.microsoft.com/en-us/download/details.aspx?id=30652

Windows 8 setup files.


The steps are:


Download and install oscdimg.exe.
Put the Windows 8 setup files in a folder. While any name will do I found C:\WIN8AIO to be a popular choice, so I'll use it.
Open a command prompt as administrator and create the ISO image C:\WIN8DVD.ISO like this:

\path\to\oscdimg.exe -lWIN8DVD -t10/26/2012:00:00 -m -u2 -bC:\WIN8AIO\boot\etfsboot.com C:\WIN8AIO C:\WIN8DVD.ISO


For more information on oscdimg.exe and its command line options see this article at Microsoft.
Burn C:\WIN8DVD.ISO and use it with Boot Camp Assistant on your Mac.