[SalesForce] How to Pass Arguments and a Callback Using Aura Method

I can pass arguments or I can pass a callback to my aura method but the syntax for passing both an argument and a callback at the same time eludes me. I would like to pass the ultimateParentID var along with the callback.

My working calling method in my parent controller:

({
    //get facilities list by ultimate parent 
    initFacilities: function (component, event, helper) {
        var formData = component.find("childCmp");
        var ultimateParentID = component.get("v.ultimateParentID");
        formData.getFacilities(function(response) {
          console.log('number of facilities for select is: ' + response.length);
            var opts = [];
            opts.push({
                value:"",
                label:"--- None ---"
            });
            for (var i = 0; i < response.length; i++) {
                opts.push({
                value: response[i].Id,
                label: response[i].Alias__c
                });
            }
            component.set("v.facilityOptions", opts);
          });
    }

My aura method definition in my child component, where the callback and ultimateParentID are parameters are defined as attributes:

<aura:component controller="VOBRequestLightningFormDataController"> 
   <aura:method name="getFacilities" action="{!c.getFacilities}" description="get facilities in System mode" access="PUBLIC"> 
       <aura:attribute name="callback" type="Function" />
       <aura:attribute name="ultimateParentID" type="String" default="0013700000Hsz8f"/>
    </aura:method> 
</aura:component>

Child controller:

({
    getFacilities : function(cmp, event) {
        var params = event.getParam('arguments');
        var callback;
        if (params) {
            var ultimateParentID = params.ultimateParentID;
            //alert("parent is: " + ultimateParentID);
            callback = params.callback;
        }
        var action = cmp.get("c.fetchData");
        action.setParams({
            "ultimateParentID" : ultimateParentID 
        });
        action.setCallback(this, function(response) {
            var state = response.getState();
            if (state === "SUCCESS") {
                console.log("From server: " + response.getReturnValue());
                // return doesn't work for async server action call
                //return response.getReturnValue();
                // call the callback passed into aura:method
                if (callback) callback(response.getReturnValue());
            }
            else if (state === "INCOMPLETE") {
                // do something
            }
            else if (state === "ERROR") {
                var errors = response.getError();
                if (errors) {
                    if (errors[0] && errors[0].message) {
                        console.log("Error message: " +
                          errors[0].message);
                    }
                } else {
                    console.log("Unknown error");
                }
            }
        });
        $A.enqueueAction(action);
    }

As written above, the callback works. I've tried the following in the parent controller calling method, which ends up assigning the Callback reference to the ultimateParentID variable:

formData.getFacilities(ultimateParentID, function(response) {...

And, if I just call formData.getFacilities(ultimateParentID) without the callback, the argument is passed successfully. Thanks in advance for your help.