JuBu: I don't think that you can write to that display in the E36, but I'll ask.. You sort of can do it in E46, but really it only works well on the 5 series... It's not just programmable, though. You'd have to have a microcontroller or something outputting to the display.
*Shrug* I know the E36 can't do it but it'd be nice just to have the clock show up there like you can do in the E46. I will see what I can find.