It's easier to do that with RouteConverter (
http://www.routeconverter.de/webstart/en) rather than with Notepad. It will still take a bit of time but probably only 20-30 minutes.
Just tell it to add a point to the map in the gap between the two parts of the ride and it will automatically insert it right in the middle and fetch the correct elevation. If that point isn't on the road, you can then drag it in the map view to the nearest point where you think it should be and it will also estimate the time it thinks you should have got there based on the rest of your ride. Then all(!) you need to do is keep on adding new points between these new points (and moving them) until you've got one for say, every ten seconds or so - that should give you a good enough line to get your distance correct.
I've done it before for a missing section - admittedly not as much as 7km worth, but still the theory is the same. Also used it a few times to correct a GPS failure when out running, where my watch (less reliable than my bike Garmin for some reason) had me suddenly jumping about 200m to my left for about 2 minutes - as though I was running through people's back gardens instead of along the road!
