Because there is no direct way to get the base value of a unit's damage, and because the damage dealt by attacks varies a lot in game (natural randomness in the attack damage, possible criticals/bash, enemy armor type and amount, etc.), unless you keep a tally by triggers of the contributions from all auras, buffs, items, stats, etc. and thus can calculate the base damage from those factors, it's impractical to make an ability like that.
Of course, if you do that, more power to you.
You might want to consider basing it on an attribute instead of the attack damage, instead.
That said, you could approximate the first ability by adding a critical strike for one attack, and the second by basing it on damage taken, not on the enemy's base attack damage.