Varien_Data_Collection

/** @var Mage_Cms_Model_Resource_Block_Collection $blockCollection */
foreach ($blockCollection as $block) { /** @var Mage_Cms_Model_Block $block */
    $frankensteinProduct = $productCollection
        ->getNewEmptyItem()
        ->addData($block->getData())
        ->setData('product_or_block', 'block')
        ->setData('entity_id', 'block_' . $block->getId());

    $productCollection->addItem($frankensteinProduct);
}