I have a champion in the infexibility department. He is 8 and starting to embrace change.
I think it's a great idea to just leave things around the house for him to discover... This has worked very well for us in the past. I do sometimes force the issue, for instance switching seats in the car with his brother. I was prepared to listen to the whining and complaining for the entire ride, and that's exactly what happened. :-)
I do, on occasion, offer a reward he wants even more than he *doesn't* want to try something or participate in an activity. Often the reward gets him over the hump...but this is a huge departure from my days of swearing I'd NEVER bribe my kids! lol
Sneakiness, in a loving way, is a fabulous strategy.