I have added this and Clouting to the next release. The script I created is as follows:
Final Phase: 9999
Code:
~ Apply proficiency tag to parent
perform container.parent.assign[Helper.Proficient]
~ Check BAB and increase if necessary
var BAB as number
BAB = round(herofield[tHitDice].value*.75,0,-1)
BAB = maximum(0,BAB-hero.child[Attack].field[tAtkBase].value)
container.parent.field[wAttBonus].value = BAB