inputの入力と出力に変換を挟ませるやり方
例
/**
 * inputの値をcurrencyCodeを元にフォーマットする
 *
 * usage:
 *  <input type="text" amount-format="currencyCode">
 */
context.app.directive("amountFormat", function ($parse:ng.IParseService) {
    return {
        restrict: 'A',
        require: 'ngModel',
        link: function (scope:ng.IScope, element:ng.IAugmentedJQuery, attrs:ng.IAttributes, ngModel:ng.INgModelController) {
            var currencyCode = $parse(attrs["amountFormat"])(scope);
            var currencyInfo =  Currency.getInformationByCode(currencyCode);
            var offset = currencyInfo.map((x)=>x.offset).getOrElse(1);

            // model から view へ
            ngModel.$formatters.push(function toView(amount) {
                if(_.isUndefined(amount)) {
                    return NaN;
                }

                return parseFloat((amount / offset).toFixed((offset == 100) ? 2 : 0));
            });

            // view から model へ
            ngModel.$parsers.push(function(amount) {
                return (amount * offset).toFixed(0);
            });
        }
    };
});