Is it possible to keep extending a long route, without the whole route changing to 'beeline' to the destination?

So I'm trying to plan a cycle tour from UK to Italy, however if I keep extending my finish route, the whole route changes. For example, if I was going from North Wales to London, then back up to Manchester, the route will auto-adjust so it ends up taking the shortest route from the start to finish. 

Is there any was to 'freeze' points along the journey so they can't be auto-moved?

Thanks!