You can kill two birds with one stone. Carpet some 2 x 4s, lean
them up against something, and put food up there.

I think that is especially effective for cats which run to the
food bowl every time you turn around. Now they will run to the
base of the 2 x 4.

Depending on the vitality of your cats, you might want to use a 1
foot thick foam rubber (or equivalent) landing area at the bottom of
the 2 x 4.

Good luck.

Here is how my friend solved this problem.  She got a cardboard box and cut a
doorway opening that was small enough for the normal-sized cat to get in, and
too small for the "fat cat" to fit in.  She put the bowl on the floor at the
back of the box.  The skinny cat can eat peacefully at his leisure and the
others won't fit in the doorway.  It's been working for years.  Good luck!
Linda
p.s.  my vet says "get rid of the open cafeteria".  Put down both bowls, let
them eat whatever they will in a 20 minute time period, and pick the food up.
Do this 2x a day and no more.  If you are standing over them for that 20 min.
time period you can keep them separated as they eat their own diet.

Supervise eating time and only feed at specific times.  I feed my cats
twice a day.  I hang out with them while they eat to make sure that one
cat doesn't eat the other cat's food.  When they are done I give them
lots of praise and pats and then wash and put away their bowls.  That's
it until the next meal time.  Occasionally, I will give them treats, but
not often.

You should talk to your vet about your overweight cat.  Your vet can
help you figure out how much you should be feeding your pets.  My first
cat was overweight because I didn't know much about cats and was feeding
her too much.  I stopped "free feeding" and started feeding her twice a
day while slowly decreasing the amount of food, all in accordance with
my vet's instructions.  She has now been maintaining her optimal weight
for the last year and a half.