jquery - Jquery - use "starts with" matching with remote datasource

Question

Wondering how I can switch the following code to use a remote data source instead of a local array. This code changes the matching to "starts with"

    $("#input").autocomplete({
    minLength: 1,
    source: function(req, responseFn) {
        var re = $.ui.autocomplete.escapeRegex(req.term);
        var matcher = new RegExp( "^" + re, "i" );
        var a = $.grep( group_members_array, function(item){
            return matcher.test(item.value);
            });
        responseFn( a );
    }
});