AngularJS - Formatting ng-model before template is rendered in custom directive

I am creating a custom directive in Angular JS. And I want to format the ng-model before the template renders.

This is what I have so far:

app.js

app.directive('editInPlace', function() {
    return {
        require: 'ngModel',
        restrict: 'E',
        scope: { ngModel: '=' },
        template: '<input type="text" ng-model="ngModel" my-date-picker disabled>'
    };
});

html

<edit-in-place ng-model="unformattedDate"></edit-in-place>

I want to format the unformattedDate value before it is entered in the ngModel of the template. Something like this:

template: '<input type="text" ng-model="formatDate(ngModel)" my-date-picker disabled>'

but that gives me an error. How to do this?