GRID column sort(DISABLE)

my grid has 4 columns, all sortable except for the third column. I dont want the user to be able to sort the grid by clicking on the header of third column. how do i do that?

i noticed that onHeaderClicked() is called when header is clicked & it calls doSort().

# how does the header object get its $name(obj.$name gives 'Header')?
# how do i make the third column un-sortable?
# is there a way to over-ride onHeaderClicked() ?

http://www.activewidgets.com/javascript.forum.20823.1/how-can-i-controle-the.html
http://www.activewidgets.com/javascript.forum.14820.1/hot-to-disable-the-sorting.html

// disable sort for third column (index=2) 
obj.onHeaderClicked = function(event, index){
if(index==2){ return 1} // cancels further processing
else{return 0} // line not needed ( for example purposes )
};