There are various options, though which ones are available will depend on the priest/bishop and your situation in particular. To give four examples from my own past of how things can work out: I (Justin) took the name of Justin Popovich as my patron saint, though at the time he was only approved for "local veneration" by the Serbian Church, and wouldn't be officially glorified until 10 years later; my wife (Cecilia) chose the name Mary of Egypt, and the priest allowed it, even though she already had a Christian name, because of special circumstances; my daughter Athanasia was given a Christian saint's name at birth, and so also has St. Athanasia as her patron; my daughter Sahara didn't have a Christian name, so in conversation with our priest it was decided that she would have a St. Stephanie as her patron. So, when receiving communion, the priest says Justin, Mary-Cecilia, Athanasia, and Stephanie.