Simply put, especially because the sail would be measured as a genoa in the PNW, I wouldn't suggest a Code Zero for a J/30 based on the lack of a masthead halyard and bowsprit (or long enough pole to make a C0 project enough). What I would do is take an older #1 and have it cut into a shape that is more conducive to reaching. It being bagged out wouldn't be too much of an issue and the potential gains are totally worth the sailmaker time. Additionally it'll give a good use to an old sail that you have laying around. If you do add one then a padeye on the deck and a snatch block for sheeting the sail with will be the only major mods to your boat that you'll have to make.
With the rig configuration that the J/30 has a Code Zero would not be able to be used correctly and for that reason I'd suggest the Blast Reacher.
