A portfolio is a great start, but how would a potential employer know you weren't lying/plagerizing/etc without some sort of technical test?
That is a cost that isn't easily quantifiable. However, the cost of wrong hires is easily quantifiable based on the time effort required to (attempt) to get a new hire going.
Considering that most companies are looking to minimize risk and the potential benefit is not quantifiable I would estimate the chances to skip the interviewing process as minimal.
if he does not know, then this means coding interviews do not actually optimize for competent people.
are you afraid to find out the latter might be the case?