A small fraction of psionics experience extreme pleasure and boosted capabilities when they spend more than an hour or so in the fringes of a jump field, where alien physics begin to leak through just a little bit. Many also develop mental instabilities. All of these effects fade out over the course of several days after the last exposure.
During an emergency, a tramp trader's engineer must do an EVA while in jumpspace. He does not know he has latent psi powers; he just knows that while on the EVA he experiences a growing sense of euphoria and power. The next day he comes up with an excuse to go back out ("I should really check on those repairs..."), and then does so again later the same day. His affect becomes increasingly manic, and his behavior worryingly bizarre. He resists any attempt to stop him from doing increasingly frequent and lengthy EVAs, and starts talking about his "big plans."
The nature, power, and manifestations of the engineer's psi powers are left for the GM to determine.