As of now, this is not possible.  Please see [this post on Meta.SO](http://meta.stackoverflow.com/questions/73792/how-do-i-add-stack-exchange-2-0-sites-to-my-cv-on-careers-stackoverflow-com) for more information.

As Korneel mentions, for a workaround, you can add your [flair](http://askubuntu.com/users/flair) to one of the text fields that support markdown (though it isn't identical to the options for the Trilogy sites).