How can I mount an EF-M lens (22mm, for example) on my Canon Rebel T4i EOS EF-S?
You cannot mount an EF-M Lens on a standard DSLR or at least it won't work the way you want it to.
The EF-M lenses are designed to sit closer to the sensor than on a DLSR. There is no way to get the EF-M lens closer to a DSLR sensor because the mirror is in the way.
You can however, put a DSLR lens on the EOS-M camera with what is essentially a spacer to keep the lens further from the EOS-M sensor (the distance it would be if used on a DSLR).
Strangely enough, you CAN fit an EF-M lens to an EF mount camera. It's just a very silly thing to want to do. Here's what happened when I tried it.
If an adapter existed, on EF/EF-S, the lens would sit farther in front of the camera body than it's designed to, and this would be like using macro extension tubes: you'd lose the ability to focus to infinity with the lens, and it would only be good for photographing close subjects. Which is why such an adapter doesn't exist.