well you seem to have the basics... I would simply expand on what you have here. Like writing tasks... like what... this could be 500 words explaining why what you did upset him... or writing on your body 5 times that you did wrong, A written apology to him for what you did, or my fav, if you have a old tape recorder or mp3 recorder recording the apology to him so he has it forever, or even video of your apology.

One of the one that i like is not being able to look at your Master for a set amount of time... not a blindfold, just you are not allowed to look at him at all, you must look away from him.

Just a few ideas.