If hiding a game doesn't do it for you, get in touch with our support team with a list of the games you'd like to remove. If it's just freebies, they should be able to take care of it right away.

If they're games you paid for, you'll have to confirm that you are in fact aware that once they're gone, they're gone for good. ;) A formality, just in case.

Either way, that should be what you're looking for.

EDIT: War never changes, other things do sometimes. I'm told that we'll no longer be able to permanently delete purchases from any user accounts – there are good reasons why we should not be irreversibly messing with our customers' purchase history, and I cost our friends from support quite the headache with this post. >_> Sorry!
We all kindly ask you to use the "Hide Game" option if you never want to see those games again. Thank you so much for your understanding. :)