L.S.
My son had this for at least a year before I found out what it was. I found an excellent pediatritian. He put my son on suppository laxatives for a while. I forget how often and for how long. I do remember that he treated the condition almost exactly as I had read it should be treated. I believe the article I read was this one:
http://kidshealth.org/parent/general/sick/encopresis.html#
This treatment was very successful, and my son has not had the problem for several years. He's 13 now. I suggest trying different pediatritions until you find one who will treat it satisfactorily.
Hope all goes well! ( :