Since there's no true accomplishment, you're effectively conducting safe practice in a painful but otherwise save way. If you're super keen on making this work, the fluff of it is unnecessary. Essentially you'll need a mechanic to determine how much XP you gained that much, effectively measuring the amount of retention you have from being brutalized for that time period. I would say a weekly roll similar to a profession check in the skill you want to train in then determine a formula to determine how that translates in to XP. You should NOT get a lot of XP for doing this as you're not really accomplishing anything or overcoming anything. Maximum XP rewards should measure maybe 100-150 points. Minimums should be really low, like 5-10 XP. It shouldn't be easy for a character to level up in a fast way like this, otherwise all of the town guard and such would use these methods and would have very high level guards all the time.