A cruising speed of close to 40, a superlative Idea Gunjira sir, with only two drawbacks: one, there is a bloody great big climb up to Ashinoko and two, there is a bloody great big climb up to Ashinoko. I know that, technically, that's only one drawback, but it was such a big one I thought I'd mention it twice.
Well, the runners start at 8:00AM at Otemachi ... so you would need to start at least 15 (more?) minutes earlier, to stay ahead of them and not get pulled off the road by the police through the traffic lights of Tokyo/Kawasaki.
Ludwig, who has done it before from Otemachi, said he will lead the group going from there, so I defer to him.
We can get very good information on historical split times, so we should know within a few minutes when the leaders will pass Tsurumi (first hand off - 21.4 km leg) and Totsuka (second hand off - 23.2 km leg) -- probably around 1 hour per leg, maybe a bit less for the first one since it is very flat.
I am thinking of riding out from my house via Marukobashi then Tsunashima Kaido (crosses the Tamagawa at the Toyoko Line) and follows the train line as far as Kikuna, and then meet the route of the Ekiden around Koyasu, 2-3 km before Yokohama Station. Again, we can designate detailed meeting places/times a few days ahead, as well as someplace at the top in Hakone to hang out and wait for stragglers (2 years ago it was the Michi-no-Eki Hakone Toge, on the short climb up after you leave Ashi-no-ko and before the turn off for Rte 20).