Someone at the Gentoo forums wanted a patch to remove part of the border between the window decorations (titlebar) and the app contents. I came up with one real quick, and it can be downloaded here. Use this at your own risk, I have no idea how well it works.
EDIT: I rewrote this patch, the first version was broken. You'll also need a second patch here.)
EDIT^3: I wrote a better(?) patch, here.
This is what it looks like: