how to add a custom column dynamically in ajax grid

I configured ajax grid and I'm getting json data from a url and displaying it in a grid. and my requirement is for each row I have to display a check box at the first column to select that entire row. so can you check the following code and explain please how to tweak it

"fnServerData": function( sUrl, aoData, fnCallback ) {
aoData.push( { "name": "more_data", "value": "my_value" } ); // Added to insert new component dynamically, but didn't worked
$.ajax( {
"url": sUrl,
"data": aoData,
"success": fnCallback,
"dataType": "json",
"cache": false
} );
}