Multiple Paged Posts in Twenty Twelve Child Theme

Greetings, WP Gurus.

I’m in a real pickle here. I’m working on a child theme of Twenty Twelve and I have a really, REALLY long categorized post that I want to break up into multiple pages. As a whole post, it would take forever to scroll through and really easy to lose your place, and I want to avoid that. I have phrased my Google Searches as relevant as I could but with no plausible results. I keep coming across the advice to place <?php wp_link_pages(); ?> into the theme’s single.php file then drop <!––nextpage––> anywhere into the post’s Text view on the Admin site, but that advice is old and relates to the structures of older themes like Twenty Ten and Twenty Eleven than to Twenty Twelve’s structure. I thought I found something in Twenty Twelve’s content.php with the following code:

<?php if ( is_search() ) : // Only display Excerpts for Search ?>
		<div class="entry-summary">
			<?php the_excerpt(); ?>
		</div><!-- .entry-summary -->
		<?php else : ?>

		<div class="entry-content">
			<?php the_content( __( 'Continue reading <span class="meta-nav">&rarr;</span>', 'twentytwelve' ) ); ?>
			<?php wp_link_pages( array( 'before' => '<div class="page-links">' . __( 'Pages:', 'twentytwelve' ), 'after' => '</div>' ) ); ?>
		</div><!-- .entry-content -->
		<?php endif; ?>

I tried experimenting with it and around it but to no avail. I deactivated my plugins and that didn’t work, either. Any help would be appreciated. Thanks.