Chronic frequent BM s/p colonectomy

I am an RD who fielded a call from a patient who is 2 years s/p removal of 20" of colon d/t cancer.  He continues to have frequent bowel movements (every 30 minutes per his report) that are not watery or loose.  His surgeon states that this should "clear up" and has made no attempts to further rule out other problems.  This gentleman has regained the weight he lost during his acute illness and denies nausea/vomiting/bloating etc.  I recommended a trial of dairy cessation just to rule out lactose intolerance, although it doesn't really sound like this is the issue according to his reports.  He does state that the fiber supplements he tried seemed to excacerbate the problem, although I believe he has only tried the soluble fiber additives that are commercially available.  Any help that may point us in the right direction would be greatly appreciated.