I face this kind of problem all the time. Every few months I change contract and begin to indoctrinate a whole new team. I use the approach of "selling by example".
I start by using as many XP practices as I can on my own. It's not "full" XP, but test-first, story-driven, frequent-release, refactoring and so on are easy to do, and even by themselves usually show a marked increase in productivity and code quality. My managers quickly get used to the index
cards with stories and tasks that I use for my own planning, and often find them easy to understand and prioritise.
Once I have gained some credibility, without ever mentioning XP, I begin the next phase. I mention how I do this stuff, refer people to Wiki and here, bring in a few books and so on. usually by then I have some people interested enough to at least consider some experiments using the more team-oriented practices :- stand up meetings, planning game, pair programming and so on.
It doesn't always change the way things work, but I have left behind me a trail of people at least interested and willing to consider it.
