Observer.php

class Sample_Model_Observer
{
protected $colToAdd = 'colname';
    /**
     * @param Varien_Event_Observer $observer
     */
    public function urapidflow_profile_action( $observer )
    {
        $action  = $observer->getData( 'action' );
        $profile = $observer->getData( 'profile' );

        switch ( $action ) {
            case 'start':
                $columns = $profile->getColumns();
                foreach ( $columns as $col ) {
                    if ( $col[ 'field' ] == $this->colToAdd ) {
                        // column present, no need to do anything
                        return;
                    }
                }

                $columns[ ] = array(
                    'field' => $this->colToAdd
                );

                $profile->setData( 'columns', $columns );
                break;
            case 'stop':
            case 'finish':
                $columns = $profile->getColumns();
                foreach ( $columns as $idx => $col ) {
                    if ( $col[ 'field' ] == $this->colToAdd ) {
                        unset( $columns[ $idx ] ); // unset column to avoid saving it in config after profile finishes
                    }
                }

                $profile->setData( 'columns', $columns );
                break;
            default :
                return;
                break;
        }

    }
  }