Fat cat and skinny cat

Last year I adopted a Sphynx cat named Mambo. He was very overweight so instead of free-feeding, as his previous owner did, I cut down his food to half a cup twice a day. Slowly he started to slim down a bit. Then a few months ago I adopted a second Sphynx, Taboo. He is very slim and I was advised by the breeder to free-feed because it would help him regulate his body temperature. Now Mambo is gaining weight again. How do I get one to loose some fat without the other going without?

I've googled Sphinx cats & find that they eat more than other cat because of being bald, & that many Sphinx owners free-feed. I can't find any statement as to what the optimum maximum amount of food is right for a Sphynx.
   
Personally, I find this omission ridiculous. I know they need more calories to generate heat, but there HAS to be a maximum amount that's good for them! SOMEBODY must have done a study on this subject! EVERYBODY knows that cats can't be trusted to eat the "right" amount of food, they ALWAYS overeat if given the chance.
   
Keeping this in mind, I have 2 suggestions.
   
1) For #1, I have a question: Can Taboo jump higher than Mambo? Lots higher? IF SO: put a bowl of food up on a high table or counter (adjustable legs are avail. from Ikea; top it with any plywood or tabletop you like), at a level Mambo can't get to. Make sure there's no step-stool pieces of furniture nearby, so Mambo can't take the height in 2 or 3 hops. Then you can feed Mambo on the floor (under the table, thus stacking the cats) & Taboo up where Mambo can't jump.
   
OR
   
2) Buy a magnetic or radio-controlled cat-flap door. Build a box (2x4s & plywood) big enough to install the flap in, with some 3x6 inch windows for light (use a jigsaw). Put the activator medallion on Taboo's collar. Put the bowl of food for Taboo's free-feeding in the box, & then Mambo can't get into it. Continue to feed Mambo twice a day as before.
   
Best I can come up with.