[xmonad] set window borders in manageHook

Hello! I want to be able to mess with window borders in manageHook (e.g. to make mplayer borderless at all times). This is impossible because of the way 'manage' and 'windows' currently work. Any ideas what to do here? I think 'manage' and possibly the manageHook interface need to be changed to make this work, and I don't like interface changes. :/ Lukas