Since the main question to ask is how do you go about providing the external link, a couple ways to do this are:
1. Use the excerpt field to insert your link in the post, and replace the_permalink() template tag in your title link with the_excerpt_rss(). Using the_excerpt() would place it in a paragraph tag, whereas the_excerpt_rss() will display it raw.
The problem with this is it’s a hack, and can cause issues elsewhere a post excerpt may be used, such as syndication feeds or archives.
2. Insert the external link as a custom field, and display the custom field value in place of the_permalink(). You could use a plugin such as Get Custom Field Values to grab the url, or a bit of code like this (assuming the key is ‘url’):
<?php if(get_post_custom_values('url')) {
foreach(get_post_custom_values('url') as $link) {
}
} ?>
Then use this as the_permalink() replacement:
<?php echo $link; ?>