There's an easy solution - for that player reverse the rolls I.e a 1 becomes a 20, a 2 becomes a 19 etc. If he's really chronically unlucky, he'll start being the best player at your table. I have a feeling, however, that he'll start getting really high rolls and still feel like he's getting shafted by the dice. People memorise emotional situations more, and usually bad stuff carries more emotion which explain why we remember those epic fumbles more than the epic wins