change bAutoWidth settings

Hello, i have my table columns with "sWidth" specified,

"aoColumns": [
	 {"sName" : "nazione_prod", "sWidth" : "100px"},
         ....

however when i "move" the table in a Jquery UI dialog(popup) i would like bAutoWidth to be turned on, since there is more screen width.
And then when i "move" the table back into the "body" i would like bAutoWidth to be turned off.
I am using ajax data that takes a long time to query, so if possible without reloading data.

I have tried this but failed so far

var oSettings = oTable.fnSettings();
oSettings.bAutoWidth = true;
oTable.fnAdjustColumnSizing(false);
oTable.fnDraw();

Thanks