NewsPage.php

class NewsPage extends Page {
  static $db = array(
		'SidebarTextAboveImage' => 'Text',
		'SidebarTextBelowImage' => 'Text',
	);
	static $has_one = array(
		'SidebarImage' => 'Image'
	);
}

NewsPage.ss

$Content
<div class="sidebar">
$SidebarTextAboveImage
$SidebarImage
$SidebarTextBelowImage
</div>

PortfolioPage.php

class PortfolioPage extends Page {
  static $db = array(
		'SidebarJobAds' => 'Text',
		'SidebarJobAdsHeight' => 'Int'
	);
	// Duplicates relation, porfolio has sidebar images
	// but doesn't allow text. But it has job ads.
	static $has_one = array(
		'SidebarImage' => 'Image',
	);
}

PortfolioPage.ss

$Content
<div class="sidebar">
$SidebarImage
$SidebarJobAds
</div>