Actually from the way you describe it, many different ways of accomplishing this feat can be used. It is not "clearly" a peek. It can be a peek, but it can also be other things. Look into impression devices. The hornet seems to be a good one, recommended by a lot of mentalists. That one is your peek, the others are more obvious ways to I guess more educated mentalists, but I wouldn't want to reveal it here in the public section of the forums since that is somewhat exposure.
I don't think it is an impression device, atleast there appears to be none used.
If you are afraid of exposing things here, please PM me and we can talk. (if you don't believe I am a Mentalist, then I can tell you my reading list of what I know)
why would he just openly tell you the methods?
why dont you take some time to read and study mentalism and theory and stuff for a while (a long
while, not a month or two) like most good magicians have. you seem to want mentalism effects that require no gimmicks, switches, funny moves, center tears, peeks, mirrors, stooges, and whatever but in truth you might have to settle for that. at least for now.
there would be absolutely nothing wrong with doing a trick that involves any of those things as long as you present it right.
but if you do happen to find a marketed effect that uses no gimmicks, switches, center tears, peeks, mirrors, stooges, or whatever let us know.