What I think you might be asking is whether an individual can communicate in a similar way to that used by a medium. That would simply be trans-dimensional communication and for some individuals that can, and does, happen. But I doubt it could happen for everyone.

There's an old saying that mediums are born and not made. If one's 'ability' to communicate emerges - even if it's not recognised for years or even decades - then it's likely/possible it's there from birth. And nobody can prove any different.