Someone named Jordan would fall into the same category as Greeks named Sotirios/Sotiria
. While, in some cases, people bearing such names have gone on to become saints, the origins of these names is from a specific feast of the Church, namely: the Transfiguration of the Lord, the Exaltation of the Cross, the Annunciation, the Dormition of the Mother of God, and Easter. Therefore, people with these names would simply celebrate their nameday on the appropriate feastday, and their patronal icon would be that of the feast. So someone named Jordan would have as their patronal icon that of the Theophany.
Of course, the Slavic tradition does not allow such "festal" names, unless there already exists a saint by that name, such as Anastasios/Anastasia
(of the Resurrection).
Traditionally in Greece, it is your sponsor who decides your patron and feast day.
Not quite. Just as common, ozgeorge, is the tradition, not just in Greece, but in Russia and elsewhere, of naming children, particularly the first-born boy and girl, after one's parents. Russian priests often will appoint a patron saint and feastday when informed of the prospective baptismal name, commonly choosing a saint of that name whose feast is closest to the child's birth date or baptismal date.