I used mtb shoes at first for road biking because I only had mtb pedals, found that I loved being able to walk around like a normal person.
The soles really werent stiff enough to prevent hot spots on long road rides, though, so I bought stiffer road shoes that were spd cleat compatible, and made pontoons out of various kinds of rubber that i superglued around the cleats. Superglue will hold whatever rubber is used to the soles forever.
Ive used brake shoes as pontoons, but any kind of rubber will suffice.