Rectal Cancer in our Dog

About a month ago, we took our 9 year old aussie/border collie to the vet because we had noticed that he was having a hard time going poop.  The vet did a rectal exam and I could tell immediatley something was wrong. He told us that Cody has a tumor, about the size of a walnut, in his abdominal cavity pushing into his rectum. At that point he was done with us. His assistant basically was the one to help us and suggest if we could maybe give him medicine to help keep his stools loose, which we are doing.  So, it's been about a month. From what we can tell he is still pooping a little. and he sleeps alot.  We are so very worried about him and really feel helpless.  Does anyone know of anything else we can do to help him? Is there anything we can give him to maybe shrink the tumor?  I really hate to say this, but we don't have tons of money, but it is just so very hard!