Spencer, you said it! That cat was so big! Poor thing. This does sound a little odd (and I never have tried this, so I'm not sure how effective it is)but, there are actual pet psychiatrists out there that may be able to help with the depression.

Although my Marius wasn't grossly obese, he was overweight to a point where it was difficult to groom his hind end area (not as bad as your current white rescue Spencer, I'm sure!!! Yikes...let us know how that progresses). Anyhow, I took him into the vet and he prescribed a low cal high fiber diet. It was Science Diet LD or something like that. It worked too! Last time I brought him into the vet (aside from the scary experience of the reaction to boosters) he was pleased to see how good my cat looked! He said a lot of owners come into the vet asking about their cat's weight, but he really doesn't see many results about weight loss. I was please with Marius! He's my white boy!

Anywho...the pet psychiatrist might be worth a consideration by the new owner of poor GraySee!!