adding extra damage dice that don't multiply on a crit
I have recently run across a few class abilities and monster abilities that add extra dice on a crit, without them doubling on the crit. For example the champion ability Instrument of Zeal. It only adds the extra damage die on a crit while using Blade of Justice or Retributive Strike. So I can't just add deadly to the weapon, but I don't know of a way to add "deadly" to the effect. I can't just roll a second die after the fact, because it would apply any physical resistance a second time. I guess I could make it typeless damage and assume that the physical damage overcame the resistance, but I would prefer to add it at the time of the toll, if possible. Is there a way to do this?