Adding an
InputGestures property is in our development plans and it is in progress. You
can track the PITS item created for this here.
In that way you can see when it is ready to be used.
The MinWidth on the first TextBlock is important to be wide enough to be longer than all of your Menu Item Header TextBlocks (to evenly right-align all of the InputGestureText values).
There may be a more elegant way of doing this; if so, please let me know!