Apple - How can I install boot camp off a Windows 7 USB flash drive?

I'm having the exact same problem. I tried holding the option key when rebooting to see if I could boot from the USB key but I could not find a way to do this, so I installed rEFIt (then rebooted twice!) and THEN plugged in the USB key and the next time I rebooted it did show up as an option to boot from the USB key.

I tried that and the windows installer loaded and it found the new bootcamp FAT32 partition. It said I couldn't install to the bootcamp partition because it requires NTFS.

This SuperUser post suggests "simply format the partition using the Windows installer's built-in utility (in other words, as part of the installation process)" so I did that continued with the install and everything works fine!

long story short. To create a boot disk on USB do this:

1. open bootcamp app contents (finder, right-click on bootcamp app at applications folder)
2. Copy info.plist file to another place (like desktop), rename the original to something like "OLDinfo.plist" to preserve a backup.
3. Right-click that copied file and open it with textedit
4. Search for a line containing the string(close to the bottom):
   PreUSBBootSupportedModels
5. Remove the "Pre" string so the line look like: USBBootSupportedModels
6. Save the file and copy it back to the bootcamp package contents.
7. Run the bootcamp and select the corresponding USB generating option that now shows up there at second screen.
8. Use the rEFIt thing as noted before.
9. Profit!