I have a prayer card that offers a prayer for the conditional baptism for the unborn. Is this possible?
No. Conditional baptism is conferred only when there are doubts about the validity of a person’s baptism or whether baptism was conferred validly (CIC 869). As for the baptism of desire, this would apply only to "those who die for the faith, those who are catechumens, and all those who, without knowing of the Church but acting under the inspiration of grace, seek God sincerely and strive to fulfill his will" (CCC 1281). As for children who have died without baptism, the Church can only entrust them to the mercy of God (CCC 1261). We must always be careful to pray with the mind of the Church; to do otherwise is to go beyond the limits of revealed truth.
But you could pray for their salvation and for their lives to be spared if they are in danger of abortion. A prayer you might consider is Archbishop Fulton Sheen’s prayer for the unborn:
Jesus, Mary and Joseph, I love you very much. I beg you to spare the life of the unborn baby that I have spiritually adopted who is in danger of abortion. Amen.