Have him on beet juice, malic acid (or apple cider vinegar) and see what it does to him. Castor oil packs are always beneficial, the pain could very well be because of parasites, and they hate castor oil. With cancer, he will have to Liver Flush at some point, but have him on the beet juice and coffee enemas, and see how he reacts to that.
Nothing beats Liver Flushing for getting out stones and liver parasites, but I had some success releasing stones with malic acid and beet juice, it will take much longer though. For very sick people, you're right, extrem caution should be taken when liver flushing.