Just hit the notes. I don't know about this piece in particular; whether there is some 'valse form' hidden throughout it that you would want to try to amplify aggressively with the rhythms, but I don't pick it up from this (boring) rec. He does have a number of pieces like that, but I don't think this is one of them. The performance practice for Finnissy and most New Complexity composers in general - except where the precision of the material, rhythmically, is sort of the point - is to play pretty freely. Getting some 'looseness' and 'improvisatory sound' from the performer is like . . . kinda the point of a lot of what a strict New Complexity adherent is doing (though of course they would all complain about being 'pigeonholed by a term' blah blah blah).
You could always e-mail him, or Pace, or Powell (who's a member of this forum), or Hodges. I dunno about Hodges but the other three are social, they'll probably respond. Pace and Powell are also Facebook denizens, you could try adding them instead of e-mail.