First off, motion can only be perpendicular to something else that is moving, or else your object must be long and thin. Why can't you just say "movement away from the object"? In which case, I'd just follow latin, which uses the accusative to suggest motion toward or away from something, then a preposition for "away from." Just pick a locative motion tense. There's no specific case for it. If there isn't a case for what you want, just make it up - but remember not to make things too complicated, or you'll never remember all of it, let alone trying to get other people to remember it.