If one of the two charts is not dependent on any control, can't you just feed it the entire datatable you'd otherwise give to the dashboard? Like:
var data = new google.visualization.DataTable();
// fill data
// Dependent chart
var chart1 = new google.visualization.ChartWrapper({ });
var control1 = new google.visualization.ControlWrapper({ });
// 'free' chart
var chart2 = new google.visualization.ChartWrapper({ });
// Draw the dashboard
new google.visualization.Dashboard().bind(control1, chart1).draw(data);
chart2.setDataTable(data).draw();
As asgallant says, you'd still be able to use DataViews ( or chartwrapper 'view' parameter ) to manipulate column selection.
/R.