(in my imagination) Baltar was rescued by the Cylons after his exile to a planet(by Adama) using his "short wave communications" that Adama allowed in return for his information to infiltrate and destroy a Cylon BaseShip...later..
"The Death and Life of Baltar"
Exterior scene: Cylon BaseShip (ominous music plays)
Interior scene of Cylon BaseShip: Lucifer enters through doors and approaches The Imperious Leader
Lucifer: "By Your Command" (bows) "I have important news"
Imperious Leader:"Speak Lucifer"
Lucifer: "It appears that Baltar is about to terminate..his human body is failing"
Imperious Leader: "The greatest weakness of their species..a short existence in a frail shell..if not for their capability of reproducing I would let time destroy them."
Lucifer: "How shall we dispose of him upon his expiration?"
Imperious Leader:" He is to be regenerated"
Lucifer: " Regenerated?, but.."
Imperious Leader:"Silence! Baltar's brain patterns and memories are to be transferred into a Cylon form"
Lucifer:" Errrrr...what series?"
Imperious Leader: "Our new humanoid series"
Lucifer: (muttering .."at least it won't be another IL series..I don't know if I could bear.."
Imperious Leader: "What was that!?"
Lucifer: "Oh..nothing,your excellency , just thinking aloud of your orders...no disrespect, but hasn't Baltar been a failure for the Cylon Empire...he was to be terminated once he led us to the humans..which he could not seem to accomplish "
Imperious Leader: "Take care, Lucifer, my orders are not to be questioned..however I will elaborate..Baltar possesses devious,treacherous qualities more Cylon than human. His knowledge and hatred of his own kind will still be of use to me...now GO! DO AS I SAY!"
Lucifer: "By your command" (bows, turns and exits room )
Imperious Leader: "Excellent.....Excellent"