Click somewhere on the route and you'll get the little popup balloon; choose 'Add via point'; and then you can drag the via point wherever you like!

Thks Richard. I think I found it by trial and error en route.

Your website has rapidly become my go-to pre-planned route planner. Used it extensively on my trip from Amsterdam to Copenhagen last month. I load the routes in to OSMAnd+ which I also use for on the fly routes. But yours are better :)

(Trouble is OSMAnd has become a real battery muncher) 

Now thinking and plotting routes for UK-Vienna via a lot of alps in Sept :)

So thank you.

Barry