Theoretically, convincing someone to abandon Protestantism should be fairly straightforward. No one disputes that the canon of the New Testament was organized by the Synod of Hippo. If the New Testament is inspired by the Holy Spirit then so must be the post-apostolic men who constructed it. To acknowledge the New Testament canon is to accept an extra-biblical Sacred Tradition and to deny Sola Scriptura and Protestantism along with it. (There are of course decent arguments made by Protestants who suggest that things are not quite this simple.)
However, even Protestants who tentatively accept this argument are not necessarily ready to swim the Tiber. To many of my Protestant friends, the doctrine of Papal infallibility seems even weaker than Sola Scriptura and I suppose I can see why. After all, it does seem a bit strange that an elderly German man living in Rome should have a direct line to God. Though there are good arguments for papal primacy, they are more complex than the evidence for Sacred Tradition offered by the Synod of Hippo. If you cannot convince a Protestant that the Bishop of Rome has teaching authority than it may be time to switch to Plan B: The Conciliar Option.
The Ecumenical councils of the early church are accepted by both Roman Catholics and Eastern Orthodox churches as valid sources of Sacred Tradition, and both Catholics and Orthodox have their own subsequent set of councils. For the Orthodox, councils and the ordinary magisterium of bishops are the only sources of authoritative teaching because they reject Papal primacy. I think that it might be easier to convince a Protestant to adopt the Orthodox position than the Catholic one. Protestantism is culturally "democratic" while Catholicism is more "autocratic" so a conciliar approach might be more attractive to a potential convert. Ideally, Protestants and everyone else in the world would embrace the fullness of truth that is to be found in the Catholic Church but accepting the teaching authority of ecumenical councils would be a huge step in the right direction. It would be impossible to affirm the teachings of all Catholic councils while denying Papal infallibility, leaving the Orthodox Churches as the only logically consistent options for someone who believes in Sacred Tradition but not Papal infallibility. Any Orthodox church would be a great improvement over a Protestant denomination because the Orthodox can claim apostolic succession and have legitimate sacraments. I say that if we can't make Protestants Catholics, we should make them Orthodox.