Zoom in as much as you can. Click on set points manually:
Click NE but close to point Y and a point will be added and the route changed between Y and the next point. Move the new point to Z. Click on line anywhere to insert points on the line, then drag the points (the line moves too) to wherever you want.
In general, editing in TRA does seem ponderous though. Earlier, as I continued adding points, the time between clicking and the newly added route segment appearing was getting longer and longer.