Wow. Well I would start as late in the day as possible, so you're doing a good portion of the driving while he is having his main nighttime sleep. As for the driving while he's awake: loads of snacks, CDs of nursery rhymes which you can all sing/clap along to, a few new toys featuring favourite things (ie for my LO this would be a few new toys with wheels), his lovey (of course). I'd plan to stop for at least 30-45 mins every 1.5-2 hrs so he can blow off steam and stretch his legs. If you plan ahead, you can probably find out which motorway service stations have play areas.
Good luck! It's 11 hours up to my aunts in Scotland and I haven't even considered doing it with Stan - think when we go we'll do it by train.