If you said that to me in the workplace, I would laugh and say, "Sure. I'll take care of it." But what you are saying is very informal. A friend or a familiar coworker could get away with it. Or your boss, because he or she is in a higher position than you.
However, if I don't know the person I'm speaking to or if he/she is in a higher position than me, then I would rephrase it. The word "ass" can be very offensive, and you don't want to offend people in a higher position or to have them think that you are a low-class kind of guy.
"I'm sorry to bother you with this, but could you take care of this case for me?" (And have a good excuse ready for why you can't deal with it. >_<)