Get the array values in javascript and populate thro' js.
function getValues (){
var myArray = '<%= arr %>';
var val = myArray.split(",");
for(i = 0; i < val.length; i++){
addOptions(document.getElementById("mycombobox"), val[i], val[i]);
}
}
function addOptions(selectbox,text,value)
{
var optn = document.createElement("OPTION");
optn.text = text;
optn.value = value;
selectbox.options.add(optn);
}