<label>
<input type="hidden" id="field_0_1" name ="param_list[0][field_1]" value="off"/>
<input type="checkbox" onchange="set_hidden_checkbox(this, 'field_0_1')"/>
</label>
function set_hidden_checkbox(target, id)
{
var hidden = document.getElementById(id);
if(hidden !== undefined)
hidden.value = target.checked ? 'on' : 'off';
}