Delve deep. Ask questions to find out what's driving them. Whether they want to be inspired or to be given irrefutable facts, you can adapt your approach once you know their motivations.
Engage them. Be clear about what's in it for them: 'This project will involve working closely with a number of different people. I believe this will appeal to your social side.' People make decisions for their own reasons, not yours.
Choose your words carefully. Use phrases like: 'let's... ' or 'shall we try... ?' If you're pushy, they'll be less likely to comply.