A temporary workaround is to install the "Empty for VNC" vkb layout, which uses just 2 lines (in Terminal, or 1 line outside Terminal) so the screen is almost all free :

- install MesInput from Nokia Store;
- open MesInput and search for "Empyt for VNC" keyboard layout and install it;
- swipe to right or left until this keyboard layout appears.

Maybe it is possible to add a null vkb in http://www.mesinput.com/, I don't know (I think it is not possible because it is needed some screen area visible to swipe from one vkb to another).