The problem these days is that most cars don't allow for alignment adjustments. Front toe is always adjustable, but toe doesn't have any bearing on the car 'falling' down the crown. You would also be hard pressed to find a good alignment tech these days as most techs know how to set the toe and little else. Maybe that's a good thing....
First thing to do is to swap the front tires from side-to-side. Some radials will cause a 'lead' to one side. Normally the tire won't have any other problems. If that cures the problem - great! If not more than likely what he needs is a little more positive caster on the right front (or a little less on the left.) Not to worry, caster has no effect on tire wear (within reason.) But instead of trying to find someone that wants/knows how to accomplish that how about trying 5# less air in the left front (or 5# more in the right?) Less air in the LF will create just a slight bit of rolling resistance and help hold the car in place on a crown.
Trying to adjust the level of assist on a variable-assist rack is a pita, if even possible (depending on model) and still doesn't address the problem - the car will still follow the crown.
If he wants to pursue adjusting the caster the easiest way will be to shift the engine cradle. What he'll be looking for is about 1/2 -3/4 degree more positive caster on the right than the left. It really isn't as difficult as it sounds, but like I said, most guys doing alignments haven't a clue.
Beav