To bad 
But if you dare you could even mess a bit with a USB keyboard, since a lot of them still support PS/2 protocol if they detect that they are not connected to a USB port.
The wiring of such an adapter is pretty simple (see http://www.tomshardware.co.uk/answers/id-2213368/keyboard-usb.html)
I did this a while ago with a USB mouse and a Teensy
vKeyboardMouse_BT
A modded Logitech mouse that sends it’s PS/2 data stream to the Teensy which normally forwards it as USB-HID-Mouse package. This way it normally behaves like an ordinary mouse. But via a Bluetooth-SPP connection you can alter the normal mouse behaviour or even send Keyboard-/Mouse-HID-Packets/-Macros from any BT device to the mouse, which then forwards them to the host.