I always sorta wondered about this. Everything in the RPG book is rather vague. I don't have it in front of me, but Sanderson's note says something about how "careful reading will reveal how it's possible to use this to use someone else's metalminds", and frankly I've never seen how that's possible.
What aluminum does is store "identity", the things that make you a personality. It stores your convictions and your beliefs and your quirks and everything that makes you, you. I'm not sure if, on Scadrial rather than in the game, it's supposed to work like copper. What do I mean by that? I don't think it's like pewter where you store strength and feel weaker, then return to normal when you aren't storing; like copper, when you put the memory in the metalmind, it's there for good and you don't get the memory back just because you aren't storing; if you put an aspect of your identity in an aluminummind (which is not a fun word to type; try it) you choose something specific, like your tendency to make "your mom" jokes, and then it stops being a part of you until you tap it again. Let me clarify; this is just my supposition, and entirely unsupported so far.
So, here's the best I can think of. It requires a central belief of Feruchemy to be wrong in a believable way; basically, the rule "only the Feruchemist who stores a trait, can tap that trait" is, instead, "no one who ISN'T the Feruchemist who stores the trait, can tap that trait." Basically, to pick examples from AoL, if Miles stored some health in a goldmind, Wayne would not be able to use it; not because he isn't Miles, but because he IS Wayne. If Wayne had the ability to use Feruchemical aluminum, he could have stored the entirety of his identity in an aluminummind (man, that word) thereby temporarily not being ANYONE; this person would have no identity to let the goldmind know not to allow him access, so he could use it.
This seems like a HUGE stretch to me, and while not technically impossible it's just preposterous, but it's the best I've ever been able to come up with from the clues we've got. If anyone has a better theory, I for one would love to hear it.