Custom Header rows for filter etc. using FixedColumns

Bardnet

I need sortable tables with fixed headers and fixed columns. I therefore want to use DataTables. I need a custom header row. It should contain input fields or select boxes to filter the content via AJAX call or FORM POST etc.

When I build my table with a complete HTML layout the header rows are being duplicated including the input fields that get POSTed twice when I send the FORM surrounding the DataTable. I understand the original header row is set to a height of zero and the visible header row is a copy containing everything incl. form fields.

I thus would like to inject a custom header row via JavaScript like so fiddle (using Handlebars.js template library).
When I finally call $.fn.dataTable.FixedColumns only the first header row is duplicated for the fixed columns leading to a strange look.

How do I now tell DataTables I have two header rows to be fixed for the fixed colums?
Should I call _fnDetectHeadermanually at a certain point in time myself? Can I add information about my custom header row to the oSettings.aoHeaderarray myself? When? Is there a callback to use?