stop keyboard disabling when the screen is folded underneath

I have an Acer R3-131T 2 in 1 laptop.  The screen can be folded right back 360 degrees to enable it to be used as a windows tablet. Like this:

https://content.hwigroup.net/images/products_xl/317576/12/acer-aspire-r3-131t-c56l.jpg

However, I want to use it the other way up, with an external monitor connected and the screen folded completely underneath to use the laptop just as a keyboard. This would be a very handy way to use the laptop with an external monitor, but, unfortunately, once the screen is rotated back more than 180 degrees the keyboard gets disabled. 

I’ve turned off automatic switching to tablet mode and it doesn’t switch to tablet mode, but the keyboard still gets disabled when I push the screen back far enough.  Any ideas as to how I can keep the keyboard active with the screen folded right back underneath?  Thanks for any help.