I know that motorcycle safety manuals say that the passenger should lean with the motorcycle/rider. Its been a heavily debated subject for years.
Myself (riding an Ultra) I prefer my passenger just sit on the bike and enjoy the ride. I find it very un-nerving when the passenger starts throwing their weight around as even when I give my kids rides (10 and 13 yrs old) I can feel every time they shift their weight or even turn their head to look at the scenery.
If you're riding a sportbike then its a different subject. (thats where I started years ago) But on a touring/cruiser I don't think the riding is ever aggressive enough in a two-up situation where passenger lean becomes a big factor.
The biggest issue with two-up riding is making sure the passenger is comfortable and trusts the rider...especially if the passenger is apprehensive about riding in the first place. If you have a nervous passenger who isn't used to riding and you start riding aggressive because you think it will be "fun" for them, 9 times out of 10 you will wreck their impression of riding and scare them to where they don't want to ride.
Take them on a nice, easy road with some great scenery and easy turns. Tell them to just sit back and enjoy the ride and to try not to squirm around alot. If you respect their apprehension and take them for a ride which will allow them to appreciate the scenery and enjoy the ride, you'll probably have a passenger sold on the idea of getting on a bike and understanding that there is no better way to see the country.