Javascript constants not allowed in models

I tried to create a numeric keyboard and stuck at the following: I want to let every button handle its own key, so I pass this key through the model:

Repeater {
  model: ListModel {
    id: model
    ListElement { label: "7"; value: "7"; key: Qt.Key_7 }
    ...

In the button component (delegate) I use this:

Keys.onPressed: {
  if (event.key == model.key) {
    event.accepted = true;
    clicked(model.value);
    ...

But the point is that it doesn't let me use Qt.Key* constants:

file:///D:/Projects/qmlinterface/Controls/Numpad.qml:25:43: ListElement: cannot use script for property value 
ListElement { label: "7"; value: "7"; key: Qt.Key_7 }
                                      ^

There are workarounds (scancode hardcoding, string-scancode hash function, etc) but all that is workarounds with overhead, complications, performance flaws.
Please implement using script constants in models.