You're right about
it being all the membership having access once you enable your email address here - sorry. The only other option that I know of is to hope they have their email enabled! For example, under my name you can see a small envelope 'lit' up - that means I have my email enabled so that all a person has to do is click on that envelope and it will bring up your email service (Google, Yahoo, or whatever service you have) with that person's email address already in it.
The other thing you can do is to click on the members name that you want to email. It'll take you to their profile where you can see whatever details they have chosen to show. There if they have it enabled, you will see their email address.
HOpe this helps some!!!