[Mathias]

Here you are (since I wrote this for something else).

Timing: UserPreAt, 100

~Count the number of hit dice
var HD as number
HD = hero.tagcount[Hero.HitDice]
~ Add to our HP
      hero.child[Totals].field[tHP].value += HD

So, to add in the extra 3 at 1st level, add those HP in on line 3:

~Count the number of hit dice
var HD as number
HD = hero.tagcount[Hero.HitDice] + 3
~ Add to our HP
      hero.child[Totals].field[tHP].value += HD