CSRF and ajax submit

[eluser]davdtm[/eluser]
Hello guys, I'm really frozen since a while on the following issue:

1) I'm using CI 2.0 with CSRF enabled

2) I've a form with the CSRF key stored within a hidden field

3) I submit (POST) the form through ajax, by exploiting the jQuery form plugin (running something like: jQuery('#form_id').ajaxSubmit(options))

Now the problem:

if the form action is set as 'http://hostname/domain/...path.../file_to_be_executed.php' everything works beautifully. However, this way I'm running an external php file, so all the CI tools are not available. On another hand, if action is 'http://hostname/domain/index.php/controller_name/controller_function' I get a '500 system error', which is due to the CSRF. In fact, disabling the CSRF I successfully run the controller which is what I'd like to do.

What you suggest to address such issue? I've found the following post

http://ellislab.com/forums/viewthread/125687/

which is very interesting but just suggests some 'double cookie submission' approach, which is surrounded by clouds for me.

Thanks for any help

David