Previous Post Link on index.php

I’ve been trying to figure this out for hours. I’ve built a theme that displays one post on the index page, and I don’t want users using the archive (/page/2/) next and prev links.

I’d like to link to the previous post, because once there, users will be on single.php, which supports next/prev post links.

Basically, I want a work around for this:
<?php previous_post_link('%link','&laquo; Previous',FALSE,'47') ?>

Without using this:
<?php posts_nav_link('','','&laquo; Previous') ?>

I’ve been trying to use something Otto wrote:

function get_next_post_id() {
global $wp_query;
if ($wp_query->$current_post == $wp_query->$post_count) return 0;
$next_post = $wp_query->posts[$wp_query->$current_post - 1];
return $next_post->ID;
}

In combination with this:
<a href="<?php echo get_permalink(); ?>" />&laquo; Previous</a>

And this:
<a href="<?php echo get_option('home'); ?>/<?php echo get_next_post_id(); ?>" />&laquo; Previous</a>

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