Backlight Change Notification?

Is there a decent (non-polling) way to get notified when a laptop panel's backlight brightness changes? HAL exports methods to set and get the brightness level, as well as query the number of possible levels, but there doesn't appear to be a way to get notified if the level changes. Calling org.freedesktop.Hal.LaptopPanel.GetBrightness() every five or ten seconds or so sounds like an awful idea, of course.

I've heard plans to use the XBACKLIGHT randr 1.2 property to do backlight setting, but I don't think any drivers use this yet. Polling /sys is just as bad (why doesn't sysfs or procfs support inotify, dammit!), and obviously isn't portable anyway (not that HAL is particularly portable these days either).