How do I stop my nephew from taking advantage of my elderly mother?

He's 26 and attending community college. She's 86 and loves him dearly. He uses her place like a crash pad and has been treating her like an ATM machine--to the tune of 500-plus dollars a month. He hasn't accepted student loans, smokes pot, and hasn't even tried to get a part-time job. He does have low self-esteem and apologized when I confronted him about the massive "loans" (to the tune of thousands of dollars now).. However, I don't know how to stop him from abusing my mother's great love for him. His father--my brother, isn't in the picture, and my mother isn't capable of saying "no" to him. However, she's not made of money, and even if she's not fully financially savvy or able to see what's wrong with this picture, she's in great physical health for someone her age, could live well into her 90s, and will need her income. Even worse, I foresee this escalating as he seems to be increasingly dependent on her largess. No, I don't think I can get her declared mentally incompetent, and don't want to take such extreme measures, but I just don't know how I can get the nephew to change what strikes me as predatory habits. Any suggestions?