It's like everything else. Show them the money. The good folks at FireDogLake have taken the trouble of setting up an ActBlue page listing every member of Congress who has promised not to support a health care bill that lacks a public option. The ActBlue page is a nice way of thanking them.
I'm pleased to report that the Massachusetts delegation is well represented. Congressmen Capuano, Delahunt, Frank, McGovern, Olver, and Tierney are on the list. If your congressperson isn't there, let him or her hear from you!