[Manly Man]

I suppose he could have eaten a dragon brain or two too many, but there are other ways in which the template can be acquired, as it is, normally, an inherited template. Perhaps, for some reason, you have a Brainstealer Dragon in your lineage, perhaps several generations ago, and through your psychic development have managed to bring forth this latent power.

I don't do this sort of thing very often, since finding an excuse other than magic to let an inherited template be an acquired one instead that isn't simply "A WIZARD DID IT!" can be difficult, going on a case-by-case basis. I'm only allowing this one since dragons do, if only extremely rarely, play a part in illithid culture. Consider your character a near one-in-a-million chance, and play with it accordingly. I don't think there's any Psion out there with an Ego Whip that could make one as big as your character's so much as flinch.