As someone who has to deal with lots of people like this, I say: don't. State the problem, that you're willing to help, and how you're willing to help, but go no further than that. At best, they'll ignore you until they're ready to change.
At worst, they'll start blaming you for their shortcomings and guilting you into putting your needs aside to make up for what they refuse to do. They will drag you down into that hole with them, and the longer you stay there, the less likely it is that either of you will get out.
You must tread very carefully in these situations...don't let pity and generosity become your downfall.