Solved Existing Win8.1Pro to boot from USB HDD

Hi, I need to make existing installation of Win 8.1 Pro x64 bootable using external USB HDD case.
I have tried to patch it with PWBoot 3.0.2, but without success (just got dialog with "an error has occurred").

Is there a way how to make it bootable from USB without new installation to USB HDD?
Thanks in advance!

I too would like to do this...

That's what "Windows to Go" is for.

Solved

So finally, I have solved the problem: I have cloned existing install of Windows 8.1 to USB HDD using WinToUsb 2.0 Beta (WinToUSB - Install & Run Windows/WinPE on a USB drive!).
The only requirement is to have another HDD on which can be the OS cloned. Then it boots from this USB HDD.