How to make restangular customGET to take second parameter?

Question

I've been trying to create a search box to list values but customGET somehow doesn't allow me to have a second parameter. Any solutions? Thank you.

customGETLIST didn't help.

$scope.load_promo_codes = function(){
    if($scope.searchCanceller !== null)
        $scope.searchCanceller.resolve();

    $scope.searchCanceller = $q.defer();
    var searchQuery = ('?code=' + $scope.registrationCodesQuery) || '';
    Restangular.one('promo_codes',$("#eid").val()).withHttpConfig({timeout: $scope.searchCanceller.promise})
        .customGET('get_promo_codes', searchQuery).then(function(response){
        $scope.promoCodes = response;
        $scope.searchCanceller = null;
        $scope.isSearching = false;
        if($scope.editId){
            var filtered = $scope.promoCodes.filter(function(code){ return code.id == $scope.editId; })[0];
            if(filtered) $scope.edit_promo_code(filtered);
        }
        if(!$rootScope.registrationTypes) $scope.$on('onRegTypesLoaded', function(){ $scope.pageLoaded = true; });
        else $scope.pageLoaded = true;
    }, function(response){
        reload = $scope.$parent.check_error_status(response);
        if (reload){
            $timeout($scope.load_promo_codes, $scope.$parent.retryMeta['base'] * 2 * 1000);
        }
    });
};