They make low kitten boxes. Yes, stimulate after eating. I used a cotton ball and held them over a coated paper plate. I just kept the kittens confined to the bath room until they all learned to use the box, which they did pretty much all on their own. I did put a poop on top and put kitties in the box a few times to give them the general idea.
You may be able to give the formula in a bowl now - just see if the little guy can lap it up yet. I had my group eating on their own (kitten kibble) by 4 weeks. I did mix kibble and formula and turn them loose (in the tub!) a few times. What fun!