"Yes... Fëanor, I'd actually already gotten as far as 'it is not necessary to attack anyone because if you hold off they will calm down and have children and then billions of Elves will eventually stub their toes and have accidents while undertaking extreme sports, causing much more total hurt and death'. The problem is that if they are let go they will return to Melkor for new orders and I assume he is not so easily out-logicked."
"That's clever," he says approvingly, "Hmm. 'Melkor, greatest of the Powers'. Every people know the powers by a different name, many different names. For example, I don't call the Enemy Melkor, you should stop calling the enemy Melkor, I think the only Quendi who call the Enemy Melkor are my father's children by his second wife who are doing it specifically to annoy me. She serves the greatest of the Powers, and at least someone must know the power she serves as Melkor. Well...does she know the Vala who kindled the Stars? By most accounts she's the greatest of the powers, and I imagine we can arrange for someone to know her as Melkor. That wouldn't normally work. But if the Enemy's fond of descriptive flourishes in his Oaths that could be used to identify another, and if the Oath was spoken by a speaker with no concept of what she was speaking..."
"For that matter, does the understanding of 'Power' admit of beings from other realms? I don't know exactly how to quantify the power of Valar but there are things and persons of outrageous might elsewhere in the multiverse, bearing epithets like 'planet-eater'; conceptual entities; sufficiently canny bearers of artifacts like the one that taught me magic..."
And so Loki tells a story from her childhood about One-Above-All, who supposedly created literally everything in every realm and world and reality at some remove or another - she edits out the part where he is supposed to be supremely loving, as this has always seemed dubious to her and does not improve the verisimilitude - "and it seems reasonable to translate the theme of his titles as 'Melkor'."
If it works, then she's chosen that interpretation, with intent, and the ambiguity is resolved and she's a servant of your One-Above-All so we'll hope he stays out of things. And she's bound for all the Ages of the world, but I don't see a way out of that. If it really works then that resolution of the ambiguity of the Oath would become the one the universe defaults to, and any orc who is aware there's a choice between Melkors could choose yours.
If it doesn't work, then I'm not sure what will happen. It is not impossible that it would cause her the same pain she'd experience on breaking the Oath, in which case I hope you are prepared to kill her immediately."
"...Does he have to hear them? He's not liable to have any trouble doing it, it's just - does literal sound have to be involved."
"I mean on the part of the speaker, I mean can I blanket Angband in silence and force him to move or stop using this method of orc control -" She turns to the orc. "Yes, you have the idea right. That and the part where if you don't hurt Elves more of them will be hurt in the long run, remember that part too."
The orc is watching this exchange nervously. "What if I don't want to say it anymore because I wish I never had?"
"I wish you never had either," says Loki. "Since you did, and you can't un-swear it, it seems like the best thing you can do is make it a thing that isn't so bad to have sworn."
I am reasonably confident that One-Above-All does not allocate his attention in any sensible way if he exists in the first place, Loki doesn't say. "Yes," she says. "- And the only Elves are the ones in Valinor, so you will not need to try to kidnap anyone here."
She breathes, a little unsteadily.
"Are you all right?" Her hand is clenched around Lævateinn. She will kill her if she has to.
Loki shakes her head. "We weren't sure if it would interact badly with the first version of the oath," she explains. "But if you're all right, if it worked, then no, I don't have to kill you." And she withdraws the shape of the blade until it's just a short stick in her hand. She offers her other hand to help the orc up.
"Well. Hopefully this process can be streamlined a little bit given the proof of concept, because I have four more and there are a lot of orcs."
"I don't think it'll work unless they want to transfer their loyalties and are grateful to learn that they can, which may not describe all of them," Fëanor says. "On the bright side, you shouldn't personally be required to do it; we are in fact capable of pinning orcs down and persuading them of alternate interpretations of their fundamental belief system, and perhaps she can help us."
"I'll still need to come by to solve their pain problem, but that I can do as quickly as I can touch them. And I'm not entirely sure they will be willing to talk to you, especially if they're skeptical to begin with of the 'Quendi' part and also without the pain relief. So yes, her help would probably be invaluable." To the orc: "...Would you like a name? I could give you a name or you could make one up for yourself."