I'll give some suggestions.
The Bios Configuration supports Ubuntu 14.04 LTS 64 bit and windows 8.1 32 bit only. So it would not be possible to install windows 64 bit.
Regarding the CSM, The Bios doesn't show CSM support, However you can enable or disable the internal UEFI shell, which makes it like a BIOS system when disabled.
Well but a typical 64bit windows can be installed on any PC that has a plain old BIOS system, so the question is if the UEFI shell is disabled does it than really boot like an ordinary old PC? And I'm not sure to what extent a 64bit Ubuntu is different from a 64 bit windows 7 or 8 boot wise?
Could you try to boot a windows 8.1 x64 installation USB stick (no need to install anything just check if you get to see the setup screen, the PE environment used for that is also 64 bit)
or if you have a windows 8 enterprise some ware and a extern HDD you can make a Windows2GO disk and boot it on the compute stick.
It would be really awesome if you could do any of the tests
For me it is very important to be able to install a 64 bit windows on the stick, I want to use it as a new part of my wearable PC system.