I don't know what the answer is but I fully agree with you about wanting to do it at home. They have Hospice for people, I don't see why an animal member of the family should be treated any worse. The only thing I could think of is to ask your vet for something that you could administer at home. You can't be the first person to want to do this at home. If the vet refuses you might ask a pharmacist just "hypothetically speaking" for some information. Or the Humane Society? Or even someone at Hospice?
I don't know but I wish you well with it and I'm sorry.