Please, help me make this kitten go poop!

Ok, so on Wednesday I took home a little kitten from the no-kill dog and cat rescue shelter I work for (to foster temporarily), my coworker had taken one of the dogs to the vet, and came back with a kitten. A woman found him on Tuesday night just randomly somwhere, we think a stray/feral mom abandoned him, there are a lot of those cats in the area he was found.

Anyways, on Friday morning I took him to the vet because he had not pooped since I'd had him. They gave him an enema, and the vet said after that, a "significant amount" came out. I went ahead and had them do a fecal on him, and it came back worm free! But he still hasn't pooped for me!

Details
- We think kitten is about 4.5 weeks old

- I have been stimulating him to go to the bathroom with a warm, damp cotton ball. He pees right away, but does not poop! He seems to try though, and he fusses a lot.

- He is fed some kitten milk (powdered KMR) and some wet kitten food, he likes it best when I mix up the KMR and then mix the liquid and kitten food together, and he eats like a little piggie. I do not bottle feed him, he seems to like lapping it out of a bowl much better.

- He can walk, and can now run somewhat too, still looks a little drunken with his walk, but his muscles are getting stronger. He loves to explore, he cries a lot when you hold him because he wants to walk around.

- To make him poop I have tried giving him some of that hairball stuff that is supposed to lubricate the colon or whatever (per the vet), but that hasn't worked either. It was suggested to me to give him something that we know causes diarrhea in kittens.

Should I do that? Anyone have any suggestions?

He is too young to use a box, so I don't have any litter boxes for him. He does not go pee unless I stimulate him.

What, in your opinion, is the BEST kitten formula on the market? I was told KMR was one of the best, but everyone seems to have different opinions on raising kittens!

No, he's not going poo anywhere he shouldn't be. He lives in a cat carrier when I'm not able to watch him (cause he's really small still), and I would certainly notice if he was pooing in there. And no, he doesn't get fussy after he eats. His belly is never hard, but his tummy always seems a little bloated-looking, like a little bit of a wormy belly, but the vet checked him for worms on Friday and said he didn't have any. I did call the vet on Saturday and they said that he should poo again by sometime today, but he hasn't yet.

He gets very fussy when I stimulate him, and it looks like he tries to go but can't. He onl pees.

No he's not a manx cross, he has a tail, a longish one for a kitten.

I've been mixing his wet kitten food in with the KMR, I call it kitten food soup. He really likes it.

Update:

On Monday, I took the kitten to an evet (because there were no other vets open due to the holiday), and he received another enema, upon which "a lot" came out, they said. They also gave me some kitty stool softener to use. My friend then took the kitten home that night to watch him for a day, and at 11:45 Monday night, he pooped by himself.

And he hasn't gone since. Even though we've been giving him the kitty stool softener and feeding mostly canned food (like the vet said to do, since it has more fiber).

??????????????????

Btw, he was born to a stray/feral cat. How would he even have a concept as to what a litter box is, and how could he be holding out for one? He did have one when he was first brought to the shelter, but he didn't seem to have any clue what it was or what to do with it.

I guess its worth a shot, but he had a box for an entire day when I first got him and he never used it.