This is already done in the Eastern Pacific. The Eastern Pacific uses the letters X, Y and Z. They have one female name for each letter, and one male name for each letter, and alternate them every two years rather than the way the main name list alternates every six years.
I think adding those three letters to the Atlantic lists would be simple, and their infrequent usage and only needing a total of six different names for all six lists would make the situation much easier.
So I'm proposing something like this:

Any thoughts?