well first off yes yahoo does that, second get a yahoo account, and whenever you do sign up at one of those sites use the yahoo account.
you sadly will never get the smap to stop going to the current email addy. i have not opened or used a certian email address for over 1 1/2 years now, still 500+ spam emails a week to it. i check it online remotely through the ISP, and just dump it once a month.