TinyMCE 4.0 – Add Classes into Format Select

With the introductions of TinyMCE 4.0 comes a new, nice Format Select which has a few categories:

Headers
– Header 1 through Header 6
Inline
– Bold through Code
Blocks
– Paragraph through Pre
Alignment
– Left through Justify

What I want to do is add a Classes Menu at the bottom (below the Alignment menu) which I can stack classes in the submenu. If I use the old fashion method:

$style_formats = array(
	array(
		'title' => '.large',
		'block' => 'p',
		'classes' => 'large',
		'wrapper' => false,

	)
);
$in['style_formats'] = json_encode( $style_formats );

The above will override everything inside my formats menu. If I print out the variable $in – style_formats doesn’t exist – formats on the otherhand does exist, but as a string. I tried to json_decode it but it was no use.

How do I add a “Classes” menu appeneded to the pre-existing formats?