Selectable without reset

Selectable without reset

I'm try to use 'selectable' on a grid of <li> items to allow a user to specify a weekly timesheet (grid of 24x7). I can almost get the 'selectable' to work for this purpose except that any previous selections the user has made are reset when the user enters some new data. Is it possible to configure 'selectable' to add to the list rather than reset it when the user starts a new selection - i.e. like it does if you hold ctrl button down? If this is possible, is it then possible to 'toggle' elements back to 'unselected'.

Thanks