Comment 7 for bug 1377096

looking at the keyboard source code - it indeed looks impossible not only to add custom symbols without recompiling - but no modifier keys are ever possible to be sent as the keyboard acts as text editor (for autocorrect, etc) and does not directly send keycode events to Mir. So there does not seem to be any straightforward way to enable modifier or any special keys.

It may be easier to implement sending direct keyboard events as a separate service and then crafting a client into ubuntu-keyboard to talk to it and use the keyboard as an UI only to send real events, like have a "^C" button, etc.. otherwise it will require a huge rewrite of the logic