RemoveEffect should work since it's all in one script:
// 87: Remove eEffect from oCreature.
// * No return value
void RemoveEffect(object oCreature, effect eEffect);
K2 also has RemoveEffectByID and RemoveEffectByExactMatch if that doesn't work.
I also forgot to mention before you should probably check if applying effects to both hands stacks when you're using a two-handed weapon.