If it were brake rotors, the vibration would be present ONLY when braking and I think the complaint would have included that information.
Since he feels it only through the steering wheel, the odds of the problem being anything other than front wheels is highly unlikely.
Yes, you must determine if the frequency is wheel speed, driveshaft speed or engine speed, but that is usually quite obvious.
If the vibration is indeed static parts in harmonic oscillation it will be at one particular speed.
Believe me the odds are about 98 out of 100 that the problem is wheel/tire related.
In the old days I used to do a reasonably good job with a bubble balancer. I had a good one and used tape weights in the center line of the rim if possible, or split the weight among inboard and outboard. On a Benz if you put all the weight on the inboard or outboard of the wheel being balanced, vibration is almost guaranteed unless the amount of weight required is very minimal.
That said, the computer balancers are an absolute god send. I got so tired of fighting with the tire stores to get proper balancing done that I searched and found a used Coats 1001 balancer. I have it setup for gram display and can balance to about 2 gram resolution in Fine mode. Now if I have wheel vibration it is a stiff spot or a bent wheel, not imbalance. These machines are fabulous inventions.
I gave away my bubble balancer and would never consider using one again.
Have a great day,