It is possible to patch and flash a bios for this board with pmpatch and FTK 0.9.5 DOS (see Coderush's guides).
My last try was bios version 1801. Sleep still ain't working though (i.e. pc goes to sleep, 5 seconds later fans go crazy, calm down, 5 seconds later they go crazy again, and so on and so forth until manual shutdown...)
Haven't tried patching the latest bios versions, I think 2403 is the most recent. Maybe I'll try it one day, but so far my sleep mode equals shutting the pc down since a reboot of my rig takes just 10 seconds.
Not the sexiest method, I know, but for my purposes it'll do.