winusb runs, then after many minutes, gives an error saying the drive is in use.

This thread is hilarious.

What error? I seem to recall the timeout. Check the boot directory to see if a grub directory was created even though it wasn't successful. If you have the grub directory, just create the grub.cfg file.

The method can be used on an ntfs hard drive partition formatted ntfs and marked as active. This would avoid the installation of grub as you already have grub2 installed, or do you? If you do have grub2, you would then just copy the folders/files from the extracted windows iso to the ntfs partition, mark it as active and put the entry in your current grub.cfg as instructed at the site. This only works from a primary partition but does work from an external usb drive.

You can download almost any bootable iso and then install it to usb using liveusb-creator to make the usb drive/flash/key bootable.
liveusb-creator is non-destructive and as long as there is space on the drive to accommodate the size of the iso it works for me. I use Fedora, but according to the LinuxLiveUSB website it is available for almost any flavor of linux. YMMV

What are you laughing at?
I often use dd to copy an iso to a usb for booting. It is destructive and you do have to repartition/reformat the usb after you no longer need that particular image, but it does work and is bootable.