Herb Cohen has a lot of ideas about convincing your negotiation opponent to make a concession. He discusses his insights in his excellent 2003 book "Negotiate This! by Caring, But Not T-H-A-T Much."
- Make the other guys believe that their delaying tactics are not helping them achieve their goals.
- Don't let them think that they can get you to give in because they're being stubborn.
- Send a message that you'll take back concessions that you've given earlier if they continue to stonewall you.
- Let them know that your last offer is better (for them) than having no agreement.