bbPress.org

Hi,
I am trying to convert from phpBB but have come across a problem.
My reply subject and content is in a different table to the normal ‘posts’ table.
The standard code in the existing conversion file joins the topics table to the posts table like this:

// Setup reply section table joins
		$this->field_map[] = array(
			'from_tablename'  => 'topics',
			'from_fieldname'  => 'topic_id',
			'join_tablename'  => 'posts',
			'join_type'       => 'LEFT',
			'join_expression' => 'USING (topic_id) WHERE posts.post_id != topics.topic_first_post_id',
			'to_type'         => 'reply'
		);

but I need to also join to the table with the subject and content, the ‘posts_text’ table.
Is this possible using the current conversion framework?
If so can anyone please help me with the syntax.

Many thanks