Enemy Hero Imprisonment/Ransom

It would be nice to be able to capture enemy heroes and possibly ransom them back to the player you got them from or possibly execute them (with negatives to morale). A third option might be to just release them in which case they'd show up on the market place with you getting a bonus with someone buys them. (A bonus you don't get if you purchase them yourself)  I'm not a big fan of just waiting for heroes to recover, as things are now.  Plus this would be a fun way for heroes with histories to show up in the marketplace, and they might cost more for people who they previously fought against, and less for old allies to buy them.