Yes I guess you can use the regular spell as long as it doesnt deal any damage.
I am not going to attempt to trigger it but this is how I would go about it: The caster and target should be saved with a unit indexer for easy triggering. Upon casting, I would add the caster to a group. Have a periodic timer in another trigger to Pick every unit in group and add hp to caster and remove hp from target every period. If caster is not casting, remove caster from group. If units in group = 0 turn of trigger / can use not equal to 0 aswell if that fits better.
Something like that. Perheaps etheral has to be considered. Also some Target(Custom value of (Caster)) variable to point to the target.
You can even configure it to do other things like reduce life drained life over time, have it drain more life if target has high percentage hp, add a drained buff if target gets drained for a certain time etc