I agree that thematically there should be both a "Captured Bounty" and a "Bounty Target/Price on his Head" cards.
I like Fickle's idea for "Bounty Target". All your ships get the one focus on attack, but no defensive bonus against the marked ship. The trouble is what slot to put that ability in? I'm thinking a bounty hunter crew makes the most sense, but all the hunters from the ESB scene are already in the game. Alternatively it could be an EPT.
Back to mazz0's idea, it seems like from the time scum got there own faction somebody (myself included) is always saying, "rebel captive should be allowed on scum ships too!" But I wouldn't expect an errata for Scum and imperial only on Rebel Captive.
Barring that though, consider there are some crew-less ships that do have prisoner holds in lore but no crew slot (IG-2000), ships with illicit slot that don't have prisoner holds (Kiraxz), so I have no idea what slot to take for "Captured Bounty". Maybe make it large ship only illicit?