Fully share a unit without breaking alliances..

I'm working on my spell and I came into a problem. I want to give the owner of the caster full control of the target unit for a duration but still allow the real owner of the target to control it. There is some func that can do that but it has to set both player's alliances to allies with shared vision and I definitely do not want that.

Does anyone know how to tackle this? Thanks in advance.

Um... I think control = vision but that's from a noobish GUI user's point of view... isn't there a full-on gigantonourmous library containing EVERY JASS command?