I would think it would be a simple matter to make a stand with pivoting wing supports, that the plane sat on. you simply set the wings on the supports and slide the plane fore and aft, until it balances how you want it to with the pivot point of the supports being the balance point on the wing. I would put some type of thin foam rubber on the wing supports that would somewhat grip the underside of the wings for security and use small ball bearings for the wing supports to pivot on. width and height, could be made adjustable. leaves both hands free to work on the plane. if designed right, it could come apart and be stored against a wall to be out of the way. it could also be taken to the flying field for experimenting with balance points on a new plane as you fly it.
hhhmmmm,.....I might just build a prototype for myself......sounds like a good winter project or good club project. might be something clubs might consider having, if they have a lot of giant scale fliers.