I believe that's incorrect, unless things have changed.

A C&R FFL, if current, allows you to purchase and receive firearms directly from the seller as long as the firearm qualifies as C&R.

Unless you register the firearm in Hawaii, you don't need anything but the C&R certificate.  Just make sure you have documentation to support the firearm is C&R eligible.  Plan on leaving a signed copy of your license certificate with the seller.

Firearms are required to be registered within 5 days of acquisition, so as long as you leave for home within 5 days of taking possession, you should be legal.  If you plan on being in the islands longer than 5 days after transferring the firearm, then you will have to go through the registration process as a visitor.

You might also consider shipping it to your home in CA.  Then you won't have to worry about an unexpected delay or scheduling problems with the seller busting the 5-day rule.

Buying and registering a C&R pistol sent straight to my home was simple.  Just call HPD if you have any questions, and don't  ask general questions.  Be very specific about your circustances.

Aloha!   

When you get into town, check out Security Equipment Corp on Young Street.  They usually have C&R type firearms on consignment.