For convenience you could make it so, that you press a "manual route planner" button and a line appears between the cursor tip and your current location (or you could just set a hypothetical starting point anywhere in the map). Hovering over any star would make the line snap to it. If the line is interrupted, than it means it exceeds your jump range and you can't click on that star to make the line stick to it. If the line is continuous than it is within your range and you can click the star and the line will attach to it. From there you draw the next line and so on and so forth, until you have drawn your route.
For even better planning, an orange continuous line means the star to which the line is connected is scoopable. A violet line means the star is not scoopable, so you can avoid those. Of course, you can incorporate unscoopable stars on your route, but the next line you draw has to be orange and continuous (means within your range and scoopable), because if it is interrupted (whether orange or violet) than it means you won't have enough fuel.
Right clicking would undo the last step. Basically you just connect dots with lines and the line type/colour would tell you whether you can make the jump or not and whether the target star is scoopable or not. A fail safe would prevent you from being able to connect an interrupted line.
Additionally, there could be a "correction" option, so that you would not need to redraw the entire route. In this mode you would click on a star within the route and detach the line. Find another star and re-attach the line to it. The line between the new star and the next en route would adjust and change in style (so if it becomes interrupted, than it means you have to insert an additional stop in between).
You also should be able to deactivate the route (and use another if the case), in case you want to jump to, say the 5th star in the route, with the help of a neutron star. From there you re-activate the route and keep on jumping as planned.
