If you ride lots and lose the weight you plan to lose, then you'll be fine. There's no specific training plan you need other than to accumulate the miles. The more miles you accumulate, the easier and more enjoyable time you'll have. Start a log today.

As Pete said, many people use the first part of the ride to get into shape. And drmweaver2 suggests you take it easy at the beginning. But since you are on a fixed and fairly agressive schedule, you probably don't have the luxury to do either of those. So you'll want to already be in shape when you arrive at the start. If time permits, try to get in 10,000 miles (5000 per year) between now and the start of your trip. Don't stress out about it however. If you can even do half that, you'll be successful (although not so enjoyably so). Include at least some long hills in your rides, as you'll encounter many of those on your trip.