[Eomer of the Rohirrim]

Well I can imagine Frodo the Nazgul stabbing Sam and Merry and Pippin and turning them into his slaves.

However, I think it would be particularly funny if, after years of discovering the secrets of Mordor, Frodo the Nazgul started forging his own Rings of Power in Mount Doom, and giving them all to Sauron and the other Wraiths. The Forces of Evil would then be entirely under Frodo's command and Frodo son of Drogo, Hobbit of the Shire, would then be recognised as King of Mordor and Undeniable Lord of all Evil.