I have never in my life bothered to speak to boarding staff or security line checkers about companions traveling with me using the priority lane if I'm eligible. I just put my boarding pass on the top of the stack or say "they're with me" and have never had a second glance, on any airline. Typically, their boarding passes do not say "priority", and they don't get priority if they're not walking on the plane / through security with me. (Benefits that actually have a cost or involve a limited resource, like lounge access or preferred seats, airlines tend to be a bit more concerned about the letter of the rule. Honestly, many here would be thrilled if any gate agent ever enforced boarding order at all. The letter of the rule gives one companion on the same reservation as a non-AS, non-AA Emerald preferred seats, waived checked bag fees, and lounge access.)

Putting your frequent flyer number in another traveler's profile seems like a really bad idea and very unlikely to help, even if AS's system didn't reject it when you put the number in. It can only lead to problems, IMO; for example, you may not be able to check in until you've removed the incorrect number. And it means they won't get any credit for the flight; they should put their frequent flyer number in (any oneworld or other Alaska partner program).

That said, are there even priority security lines at any AS airport? Most American frequent flyers use TSA PreCheck, and a lot of airports have eliminated priority security in favour of PreCheck; if you're not American/Canadian, you may well not have jumped through one of the hoops and paid off one of the agencies you need to jump through to get PreCheck. PreCheck lines are sticklers: if your boarding pass doesn't say PreCheck, you can't use the line, unlike priority security (which is just a different line for the same regular security checks) or priority boarding or check-in. (These days, I have PreCheck but not priority security, so I don't usually check carefully for priority, but I recall it being mostly gone at US airports.)