This one is interesting because they have no stats, therefore can't do anything. So, why would you want these slaves if they can't do work? Under a first time play condition, the player doesn't know that they only have two chances to sell slaves and many, many more chances to get caught and those almost always result in an automatic loss. It's sort of a sucker punch from the author.
I imagine Duke is Han Solo with the serial numbers filed off. It doesn't make a whole lot of sense for him to be keeping slaves. What are they doing as he jets around the universe? If he buys people, wouldn't prospective hires wonder if doing a bad job will land them in a cage? It just doesn't work in my mind.
To alter this scenario, a simple change is needed. Give the slaves stats. There are only 6 professions in the book: Pilot/Navigator, Starship Gunner, Bodyguard, Skimmer Driver, Engineer and Medic. Assigning a number to each gives the slave a set of skills and statistics.
But what good is that? If Duke purchases a slave then sets that person free, they may sign on as crew. I would suggest a Cunning roll for this. It isn't that Duke is tricking the person, Duke is pitching a glamorous life on a starship. Duke is a business man and expects these crewmen and women will work one week for free. At the end of following week, if he doesn't pay them, they will walk off. He doesn't get a second chance with a Cunning roll because they know he is free-wheeling with promises based on the first one. One thing they would NOT get is a death payment.
Now the flipside. If Duke DOES NOT free them, every time he gets into trouble the slaves will try to make a break for it, either joining the enemy, seizing the ship or taking the hopper to escape. Every time someone isn't guarding the slaves when trouble starts, Duke has to make a Cunning roll to avoid this. Every darn time!
I kind of like this idea. One other advantage of this change is Duke is not permitted to take a Skimmer Driver off their homeworld. They just won't go. In this case, a freed Skimmer Driver will travel with the crew of the Antelope.
In this run, Duke has 750 secs to start and a Cunning of 3. He decides to spend about half of his cash on 3 slaves, then sets them free. He makes his Cunning roll twice, but misses the third. It turns out that the two people willing to stay on a crew are a pilot/navigator and a medic.
I am not sure how to handle their papers. Perhaps they kept them or the slaver gave them to Duke when the purchase was made. Neither one seems right, but that's what I am doing.
The only other mod to this is ignoring the line about slaves in r335 and r339. Obviously, Duke could be a slaver and sell them, but it seems weird.