Hi Andrew,
Sounds like a great trip!
In nroute, with the route active...
- right-click on the route line on the screen between the points where you want to alter the route .. when you right-click on it you might also get some other map features listed .. right-click on the route name,
- click on "Insert route section",
- you will see the mouse cursor change from the pointer or hand to a route tool and you will see a black line from the start point of that section to the route tool and from the route tool to the next point in the route,
- simply click on the point you want to divert the route through and it will automatically be recalculated.
The secret is right-clicking on the route line of the active route between the points where you want the diversion and right-clicking again on the route name to get the context menu with the "Insert route section" item. After that it's really obvious and quite easy.
...ken...