De-authorizing without access to a library?

Ive had a string of bad luck and need some help. Over the course of several years, I've registered 5 iTunes libraries, but now only have access to 2 of them. (Had 2 hard drive failures and am letting my sibling use my laptop for an extended period at college)

Anyway, I dont have access to the libraries I want to de-authorize. How do I de-authorize a library I dont have access to?

Yes, I could start a new iTunes account but I'd lose all the music that I have in 2 of my libraries. Please tell me there's some master account page with the ability to radio-button de-auth various computers 🙂

Thanks!