This topic is of great interest to me as well. I have a file as thick as my wrist on this very subject.
There are very few papers on the connection between diet and MM, but the ones that do exist are fascinating, in my opinion. But more to the point of your question, allegedly curcumin (turmeric) kills MM human cell lines in vitro. I take this supplement every day--more than is recommended.
If you do a very thorough search of clinical trials regarding MGUS and MM, you will eventually find some trials that involve administration of NSAIDS daily, ascorbic acid, and probably curcumin.
Just speaking for myself, I take NSAIDS, curcumin, B-12 and Vitamin D supplements daily. I've seen some good data on green tea, but I don't drink it, unfortunately. I need to start!
Mike