It just dawned on me as well, he's not tapping, but actually fretting as the marbles hit the strings giving the bass that mildly slappy sound.
If this guy did a CD, I'd buy it no sweat, I really like the "early Oldfield transported into the present"-character of his music. And his mad scientist-spiel of course, plus he really seems to enjoy what he is doing and is not sour-faced about it.