If you don't mind me intruding on your conversation with Jim, I see a few of problems with your suggestions.
1)By avoiding whatever reason Jim has planned for said genetic treatment to be a one-time/one-individual thing you make the whole choice void. If you'd be able to make several doses that would work on several Vanaes/random males, what will stop you from including yourself?
2)While PC will definitely have an option to become palls with some Black Void members during Kara's Second Quest, those are from the Myrellion branch. They are also likely to become blacklisted by another Black Void group due to the Saendra business. Lastly, PC is supposed to be a free agent pursuing his inheritance, and while atm. nothing prevents them from spending a lot of time in one place, they can't really settle down to oversee an operation like that. They have nobody to do it for them either, as Jim has pointed out.
3)I agree that forcibly transforming a tribe of Vanae is something Hardass Steele may decide to do, but I fail to see any reason for that newly made all-male tribe to welcome PC, so it won't result in reverse-harrem.
The problem and why i'm so insisting on more than one is that it would doom the race to incest in subsequent generations that would result from having only one male parent. Specially considering the weirdness of Vanae genetics.
The solution is pretty simple. There is a limited amount of genome and not all transformations are the same. I assume that a gender reassignment transformative for a specific races takes considerably less resources to make than a racial reassignment transformative, even for someone like Steele with his special nanomachines. In one you'll just have to change one chromosome, while in the other all of them.
The essence of what I'm suggesting is that the players would bring the Vanae Genome key to different geneticists, to get different options based on their expertise:
* Mischievous: Julian Haswell or whoever Jim was thinking. Use the genome to make a transformative to yourself, that only works because of the PC's nanomachines. This solves the problem of the cum-hunts by forcing vanae to have sex with you if they want to have male babies.
* Nice: Byron McAllister. Use the genome to make 10 doses of vanae-specific transformative and distribute it to vanae that are willing to go through that process. This solves both the problem of incest and the cum-hunts by creating a healthy gender for the race, but still limited in number.
* Hard: Maybe Dr. Lash(convincing him by claiming that it's to punish sexual predators would have be hard work, but possible). Use the genome to create a transformative disease that only affects Vanae and infect the Sky Tree with it, slowly converting all Vanae that eat from that tree into dudes. This completly solves any problem by sending out these males to the clans around the M'henga.
We don't know if the tribe would know that the PC was responsible for this action, and if it did the player can give a hard but honest answer, kinda like Bess/Ben requirex to progress through their story but stronger. There's a multitude of possible answers that could explain this.
The whole point of having the genome transferable to one individual increases the specializes of it, and by extension, the feeling of awesomeness that you, PC Steele, can fix the problem with your dick. Which is the preferred route of solving shit that most players like. Alternatively, the option to give someone *else* said power and ride their cock, or send them off to knock up vanae huntresses independently of you, is not ruled out. The whole fantasy is utterly ruined the moment you allow it to be a free-market thing, meaning cock-wielders can come in and be *just* as special as the PC. While it's high minded to get help with the cause, it's a real kick in the boner fuel tank, which is sort of the point of the whole game, really. I'm certainly not going to fuck with said setup just to make room for a nonsensical slaver fantasy that can be catered to in other ways and places.
Some female Vanae could become the enforcers themselves under the promise of getting free babies. But I don't particularly care for the Slaver suggestion, it was just a suggestion for setting up a brothel.
The more interesting solution that involves the "creation" of multiple male vanae would be to discover their origins, go to their homeworld and reintroduce the divergent races to each other. This is, of course, a ludicrous amount of work even for you, but might be worth looking at for a long-term project while this provides a fun solution in the short term.
The PC doesn't necessarily have to go to their homeworld. A Octalian could just as well come to them at later levels and give a quest. Maybe a diplomat that wants M'henga to be declared a Octalian colony, so they can pressure the UGC to let them in the UGC or borrow a gate so they can connect to the rest of the UGC to their homeworld. They would need to convince a few Vanae clans to consider themselves colonies, kinda like the Terra and Embry species thing Jim wrote.