multiple categories: not possible? Answered

hey! i just wanted to know if and if, how, it is possible to add an instructable into multiple categories when publishing.
or if it does'nt work (which it apprently does not), why not?
i had the following "problem" several times already:
imagine i would post an instructable for a necklace made from reused paper. when i want to publish it, i now have to make the choice if i add it to category "paper", "jewelry" or "reuse". this choice it not always easy, i have to think if i (in this case) would think it more important that the thing is made of paper, or that it is made from reused material, or that it's jewelry.
hope i made my problem clear!
thank you