How about doing it on a bank holiday weekend, eg May or August and then you on the way back to London you could stop off on sunday afternoon somewhere, have a bit of a show and shine (with time to clean the car) give out some prizes, camp overnight, then head off on the bank holiday monday.
How about "The Wolfsburg Run" as a name, or better still, have a run across to Germany, "back to the factory".
If you're going to Germany, you could call it "The Bahn-stormer" (after the autobahns)
Sounds like fun. But you'd have to keep it affordable, enough to cover some decent prizes (free tune ups, an engine swap of your choice, respray, alloys, mod chips from AMD, cash prize) and all the admin too.
I don't think the police would be too keen on prizes for the fastest round trip though.
