gistfile1.php

<?php
function set_page_for_post( $query ) {
	/*
	 * Only run our query modifications if;
	 * This is the main query (not a custom WP_Query or similar)
	 * We are not on the admin screen
	 * It's a single post entry
	 * The post type is 'post'
	 */
	if ( $query->is_main_query() & ! is_admin() && is_single() && 'post' == get_post_type() ) {
		$page_value = isset( $_GET['random_var'] ) ? $_GET['random_var'] : false;

		if ( ! $page_value || $page_value == 'all' || false === intval( $page_value ) ) {
			return $query;
		}

		// Set the paged value for the query, and the query_vars, this is the pagination variable used by WP
		$query->query['paged']      = $page_value;
		$query->query_vars['paged'] = $page_value;
		
		// Define this query as a paginated entry
		$query->set( 'is_paged', true );
		
		// Return our modified query
		return $query;
	}
}
add_filter( 'pre_get_posts', 'set_page_for_post' );