Hide the "Trackback" checkbox from a custom post type

Ok, got a question for the gurus. I have a custom post type that I've opened up to a custom user role. I am removing any features that I don't want on the screen for this custom role (members of a membership type of site). One of the things I can't find any help on is removing the "Allow trackbacks and pingbacks on this page." check box. I want to leave the "Allow Comments" check box. Changing settings on the Discussion Settings page does not remove it. Can't find any hacks for this one. Any ideas?

Thanks!