You can "right-click" on the map by tapping and holding the stylus on a point on the map. You then get a pop-up menu with three options: "Tap Point", "Waypoint", and "POI". In either of those three options, there is an option called "Download Route to..." that will pop up the "Download Route" dialog with that point's lat/lon automatically pre-filled into the "Destination" field.

In your case, it sounds like you want to download a route to another waypoint, so tap-and-hold on a waypoint and select "Waypoint | Download Route".