Can't boot on 1/3 from usb stick

[gmstraighter]

I'm trying to put the Windows 8.1 Enterprise evaluation version on a 128GB usb-3 stick. This boots fine on 2 of 3 computers. But the third computer just hangs without ever loading Windows - it freezes on a black screen with a cursor in the upper left. I suspect this may be because the stick isn't formatted gpt with a efi system partition (the two computers that work are bios), but if I do so before trying to install, wintousb insists I must format the stick before proceeding. It then creates an msdos partition table with just one ntfs partition.

So, how can I get wintousb to respect the partitions on the stick before install? If that's not the problem, how do I get it to load on the 3rd computer (which has no trouble in general booting from usb)?