Ok, you can use a DataView to get around the problem. In the view, you use calculated columns to return null for the annotation and annotationText columns. As an example, if you had 4 columns (1 date, 3 data), you would use this:
var view = new google.visualization.DataView(data);
view.setColumns([
0,
1,
{type: 'string', calc: function (dt, row) {return null;}},
{type: 'string', calc: function (dt, row) {return null;}},
2,
{type: 'string', calc: function (dt, row) {return null;}},
{type: 'string', calc: function (dt, row) {return null;}},
3,
{type: 'string', calc: function (dt, row) {return null;}},
{type: 'string', calc: function (dt, row) {return null;}},
]);
var chart = new google.visualization.AnnotatedTimeline(document.getElementById('chart_div'));
chart.draw(view, <options>);
Each data column is followed by two calculated columns of type 'string' which return null.