TableTools - Define export columns programmatically

Hi

I know I can define columns to export with: "mColumns": [0,1,3,4,5,6,11,12] inside "aButtons".

But I need to define colums to export programmatically depending on user profile.

I know I can use: "fnClick": function( nButton, oConfig, flash ) { ... this.fnGetTableData(oConfig); }

to catch event ad do something. But how can I "modify" the oConfig object to define that?

thanks