Add multi store support to Magento MegaMenu.

category.php

// File: /app/design/adminhtml/default/default/template/mgs_megamenu/category.phtml
// append at line #3 directly after the "$category = Mage::getModel[...]" line.

// HACK: Allow us to use root categories not part of default store
$mmId = $this->getRequest()->getParam('id');
if ($mmId){
	// Use the first selected store ... hopefully this won't be a problem.
	// We should be creating seperate menus for each store anyway. But this
	// could be an issue when we get into localization.
	$mmStoreId = current(Mage::getModel('megamenu/megamenu')->load($mmId)->getStoreId());
	if($mmStoreId !== 0) {
		// Override category
		$category = Mage::getModel('catalog/category')->load(Mage::app()->getStore($mmStoreId)->getRootCategoryId());
	}
}

...

The problem with this solution is that is requires you to save first before selecting category.