Although this paper is addressed to vets, perhaps you can find some useful info in there: http://www.vin.com/proceedings/Proce...6620&O=Generic
They mention possibly using lactulose to deal with constipation.
The Zentonil is best given on an empty stomach (an hour before or 2 hours after eating) and shouldn't be crushed, which exposes it to destruction by stomach acid.
A feeding tube would be the best option, so perhaps you can look into financial aid from one of these resources:
Info on feeding tubes: http://www.catinfo.org/?link=feedingtubes
If that truly is not an option, here are some links dealing with anorexia in cats:
And here is an excellent resource consisting of many other people who have been in your shoes: http://pets.groups.yahoo.com/group/F...isted-Feeding/
All the best to you and Shadow! Let us know how things go.