What you're talking about sounds to me a little like flashback technique. Though in flashback technique you start in simple past (he was, he did, he said) and to let the reader know that you are moving even deeper into the point of view character's past, you use past perfect (he had been, he had done, he had said).You only use the past perfect for a short while at the beginning of the flashback, though, and then you start using simple past again because the reader generally more comfortable with that.
In your case, you have a few choices.
1) You could start with present (he is, he does, he says) and then go to something between simple past and past perfect (DRAT! I can't think what it's called) where you say he has been, he has done, he has said (a sort of present past, if you get my meaning) and then after a sentence or paragraph or two, slide into simple past.
2)You could try to convey the protagonist's uncertainty and confusion in simple past and not worry about changing tense (using present doesn't really help you convey confusion and uncertainty--the images and details you select as you describe the protagonist's experience are what really do that).
3)You could start with present and after a scene break use simple past, and hope no one notices. If the story's compelling enough, probably no one will.
Anyway, those are some possibilities. Just don't expect too much from present tense. The verbs are only as effective as the rest of the words let them be.
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