You know what works really well? A small piece of a beer can. Just a tiny sliver. It keeps mine tight yet it spins perfectly.
thats what i do also thick grease where bearings press in
If he has wobbles the hub is off center already but in a less predictable way. If you're using a can it won't be off center by any real noticeable amount. The other thing you can do is just grease the living sh*t out of the hub around the bearings. This fills in some gaps and keeps the wobble from being noticeable.