Sure. As for a saint, you can pick any saint you wish. You might look at your friend's life circumstances and choose a saint who has a particular interest or patronage in those areas (e.g., St. Joseph
for a husband and father, St. Thomas Aquinas
for a teacher). Some "all-purpose" saints for conversions might be St. Monica
, mother of St. Augustine
; and St. Jude
and St. Rita of Cascia
, patrons of impossible causes.