Unfortunately, the wonderful blockUI plugin doesn't grey out the full background on short pages. I tried the $.blockUI.defaults.allowBodyStretch = true; but that doesn't help (FireFox 3.5.7 on Ubuntu 9.10).
Digging a bit deeper with Firebug, I noticed that the grey overlay carries a property of position: absolute while other tools that grey out the background (like. e.g., UserVoice) use position: fixed. Consequently, I tried $.blockUI.defaults.overlayCSS.position = 'fixed' but that doesn't find its way down to the style used. Can anyone help?