Remove the special damage bonus skill tables for bare-handed and martial arts combat. In place of them, scale up the die size based on skill: bare hands damage is a d2 at unskilled, a d3 at basic, etc. and martial arts doubles this die size, for a d4 at unskilled, a d6 at basic, and so on up to a d14 at grand master. Note that this still gives pretty poor damage output. Possibly it should be 2 dice being rolled (with the die size changing as described here).