What about subscribing for all the cosmetics for a particular month, with calendar expiration?
All would be way too much. What I'm suggestion is a complement to that, give something a little extra for those who want to get some limited time exclusive stuff and work up some 'credit' to get something truly exclusive. It's really quite a simple system that is used across many industries and products.
They only release cosmetics once a week, and noone buys all color variants (apart from the frontier charity people anyway). Probably not that insane.. quite a good incentive for people to pay the month fee for any larger items if they get a whole heap of stuff they wouldn't have bought anyway for the same price?
Look if you really want to support frontier, just buy what you want. Go buy duplicates on multiple accounts even. Trust me when you have 3 accounts with cosmetics purchased for the last thing you want is to star citizen like throw money at them. You kinda want them to invest back into the game. Keep buying arx you'll get there too.
That's the thing, I think the perspective that you're framing it (not saying it's being done maliciously btw) is one of the reasons why I'm suggesting this. This isn't about being, as you put it, a 'charity' supporter of Elite, and definitely something far from selling ship jpgs or anything related to pay to win - perish that thought. It's about providing a viable avenue for someone to support the game while incentivizing Frontier to be more active in relation to certain cosmetics, which actually works to achieve both ends, and maybe even provide some extra focus on some areas that could benefit.
I'm not buying cosmetics 'just to support Frontier', and while I'm not going to tell anyone else how to spend their own money - that's entirely everyone else's own business, I will say that the suggestion to just buy extra accounts as a way to support the game doesn't necessarily help in the best way either. I'd much rather there be extra Fleet Carrier kits or interior schemes and stuff like that which would benefit everyone who would rather not have multiple ghost accounts and would rather there be more cool stuff overall.
Maybe I'm talking about something a bit too behind the scenes business wise. Anyway, take a look at Rocket League for something
similar to what I'm talking about. It's number 23 in the Steam Chart so it's reasonably successful game that has used this sort of strategy to grow and retain its userbase. Obviously, the game is the most important part of it, but I'd daresay that it's helped the devs ensure that game is the best it could be.