Angular: Dynamically change JSON request

I'm using Angular and d3 to create a dashboard application. Some important structural pieces are:

1. A timeframe controller
2. d3 directives (i.e. d3-choropleth for example) that are used through specific controllers.
3. A JSON $http service that grabs data and pushes it to the individual controllers.

That's my structure so far. My question is: How should I go about implementing the timeframe functionality into the rest of my application? The value of the timeframe controller/form is stuck in it's own scope. Should I transfer the timeframe data to a global variable, and then somehow bind the variable to the JSON request service?

Here's my service:

// Service for making JSON requests
myApp.factory('requestService', function($http) {
   return {
        getDownloadsLineData: function() {
             // Return the promise
             return $http({
                        url: base_url + downloads, 
                        method: "GET",
                        // These parameters are dynamically changed by 
                        // a global timeframe control
                        params: { start: '2013-01-01',
                                end: '2013-02-01',
                                interval: 'month',
                                country: 'US',
                                location_bin: 'countries'}
                     })
                    .then(function(result) {
                        // Resolve the promise as the data
                        return result.data;
                    });
        }
   }
});

Timeframe controller:

myApp.controller('TimeframeCtrl', ['$scope',
                                   '$cookieStore',
                                   function ($scope, $cookieStore) {
                                   ...

Example of one d3 controller:

myApp.controller('DownloadsLineCtrl', ['$scope', 
                                       'requestService', 
                                       function($scope, requestService){
  $scope.title = 'Downloads over Time';
  $scope.tooltip = 'Test tooltip';
  requestService.getDownloadsLineData().then(function(data) {
        $scope.d3Data = data;
    });
}]);