Various things are about that specific Elf. That leaves the option of espionage from the main division of Angband, and I have nothing against the Elven residents of Valinor either.
That's about the size of it. He talks a good game about defeating the Valar and splitting the galaxy with me and blah blah blah but he actually spends all his time doing unconscionable things.
He wasn't there very long before I iced his ass, and in that time he did have terrible ethical standards for his werewolf experiments.
You could offer to go to Angband.
Look, if he wanted me to go yell rude things at a beach we might be able to manage, although I'd probably want to check how Ulmo answered a question he may have gotten around to answering by now first. I feel like Angband would be an extremely unhealthy environment for me to get anything done in.
Could offer to work from Angband but insist they stop the torture? I think he mostly does that for fun, not for strategic reasons, so he might be amenable. Or would being surrounded by dead-eyed suicidal broken Quendi who aren't actively being tortured still mess with your psychological - wait, that wasn't actually a rhetorical question when I started asking it but by the end of the sentence it totally was.
I mean, I know they're there. Could be a tossup in how it affects my work, honestly. But proximity allows mindfuckery and that's a problem, potentially an irrecoverable one.
It'd have to cover absolutely everyone capable of it in the place and a locally broad definition of 'mind-affecting magic' - I was horrified the first time I learned osanwë existed at all, for instance, I can live with communicative telepathy but that's it. And I wouldn't care to stay there literally all the time, I'm not an Elf and I miss people if I don't see them for five years. But merely being physically located in Angband is not necessarily intolerable even if occasionally I have to look at suicidal people.
Thanks. I think. There may be some reason this would still be a horrible idea, it just hasn't come to mind.
The Elf you're unwilling to hand over to Sauron is fated to a hopeless campaign to fulfill his word that starts to look increasingly like repeated attempts at suicide-by-other-Elves, massacring his way across the continent until the name of his house is synonymous with crimes we thought only Melkor could dream of, until at last he's free of the oath that restrains him from ending his life. Don't hand him over to fate either.
I'm not planning on handing anyone over to fate. It just depends on what shiny things I need to pick up in my galaxy to bludgeon this universe into behaving.