Add this to your functions.php or functionality plugin

single-id-template.php

<?php

function my_single_template_by_post_id( $located_template ) {
	return locate_template( array( sprintf( "single-%d.php", absint( get_the_ID() ) ), $located_template ) );
}
add_filter( 'single_template', 'my_single_template_by_post_id' );

Functions allows for the use of templates for individual WordPress posts, by post-ID. For example: single-689.php

See also this discussion which encourages the use of custom post-types.