You could do it on the older TomTom models, but not on a Go1000 or anything newer, I'm afraid. (TomTom call this 'progress'!)
On the Go1000, you just get 3 or 4 "waypoints" that you can add to a route calculation, and you have to input those manually on the device screen.
In the old days, you could export the planned route from Google Earth, Tyre, TT route planner etc. as an itinerary file, and load it straight onto the TomTom.
But TT have not seen fit to include Itinerary functions on all their latest models.
If that irritates the hell out of you, like it does me, please give TT Customer Services a ring and complain about it. That usually seems to be the only way to get them to re-consider their decisions.