Life Drain

Is there an easy of way of making life drain behave like siphon mana? When i set values for both life given and life stolen, it will still only let me cast the spell on enemy units. I don't even need the life drain for that specifically, but i need a channeling spell that targets a unit (only ones i know of are drain and siphon) I can't use siphon because it won't work if the target has no mana.

theres a spell under neutral hostile --> heroes, called Channel. this is a very versitile dummy spell