Feeding the "obligate carnivore" (who doesn't know that's what he is)

How does one convince a cat, who is supposed to be a carnivore first
and

foremost, that dry food is really not good for him? I've read the book
by Dr.

Hodgkins, and agree in principle with everything she says about
starting a kitten

off right on wet food, etc., etc. But she conveniently doesn't mention
how to

retrain a cat who has grown up on a diet of dry food.

When I adopted Bo, he was almost 2 years old, and had managed to
survive on

a diet of Kit-n-Kaboodle up to that point. When I brought him home, I
bought the

least objectionable dry food I could find, which he liked well enough.
I started

off by putting little drops of canned food on top, and he would eat
around them

and leave them sitting in the dish. After a week or so, he ate the wet
food off

the top first, so I thought we were getting somewhere. We eventually
got to the

point where I'm feeding him a small 3 oz. can in the morning, and he
will eat

most of it and walk away. He comes back in maybe half an hour, begging
for

food, but won't eat it until I sprinkle a few pieces of dry food on
top. Even at

that, he will eat the dry food and maybe a bit more of the wet food,
but he still

leaves it in his dish. Although he has fresh water available to him
all the time, I

noticed that he is lapping and sucking all the moisture out of the wet
food, and

holding out for the dry food. Kind of like the kid who eats just the
middle out of

a peanut butter and jelly sandwich.

So do I just leave the wet food in his dish until he eats it? Somehow
I get the

feeling he can outlast me. How long does that stuff last without
spoiling? Or

more importantly, until it becomes very unappetizing to a cat? Do I
just give in

and buy the best quality dry food I can find? I tried the Wellness
Core food, but

he won't touch it. Do cats like a huge variety? My dogs always ate the
same

thing; the vet said it was better for them. When I find a food Bo
seems to like, I'll

buy a few more cans, only to have him turn his nose up at it 2 days
later.

Sorry for being so long-winded, but I would welcome any suggestions
for

solving this problem!