Legally there must be a beneficiary, or you don't have a trust. That's the entire purpose of a trust.
He could change the existing beneficiary to be the buyer, and they'd transfer on a Form 5.
Or at least that's how it should work at the federal level. No idea on the legal requirements of the state, but I wouldn't think it would matter who the beneficiary was (as in no requirement it's a relative).
ETA: is the person the only trustee? Or are other parties involved. Technically he could add the new person as a trustee and beneciary. That way the person could immediately take possession. I believe there's a requirement that a person can't be the only trustee and beneficiary, so when the guy dies, they'd transfer to the new guy. The "perfect" scenario (if it's legally possible) would be make the new guy a trustee now, and set the beneficiary to be a different trust which has the new Guy as a trustee.