I really liked the suggestion of showing empathy and commiserate a little bit. This is a tip that works in many situations since is what most persons are, consciously or not, waiting for. Thanks for remembering me this.
I agree, and I would also suggest looking for ways you can show respect or admiration. This kind of situation will arise whenever you choose a challenging path of self improvement, whether you successfully quit smoking, lose weight, or control your finances. Those who have not found the will within themselves to do the same will see your success as proof of their failure.
One of my good friends eats too much, drinks too much, and spends too much. She is an absolute joy to be with because of her spontaneity and her huge heart of gold, but she can also be very touchy regarding her weaknesses. I was traveling with her last summer and we had dinner at a world famous restaurant. I ordered a glass of wine and a healthy, reasonably priced dish that sounded good. She ordered the most expensive and calorie laden thing on the menu, plus dessert and wine. She then proceeded to justify it, loudly and assertively, for several minutes.
I had not said a word, but I've come to accept that just BEING my healthy frugal self is enough to trigger her shame at times like this. Now I counter by casually bringing up her many strengths and praising them. How I envy her social grace and popularity. Her dramatic boho style. What a caring parent she is. How much everyone loves her. Etc. Gently, gently restoring some balance to her mood.
Not all relationships are worth this much effort, but for me this one is. If you are stuck with these roommates for a time, it may be worth your while as well.