Yes, but it will only work in more advanced email clients like Apple Mail and iOS. What is Progressive Disclosure in HTML Email Design? | Campaign Monitor
A strategy point...email should be a vehicle for action, so if the content lives somewhere else (like your site), why not use the header or teaser content to point them back there?
It's definitely possible--you'll just have some inconsistency in how it's applied across all email clients. Do note that coding this kind of feature is not for the faint of email-hearted. That said, a couple of examples are here:
Thanks Jason, Courtney,
As I suspected. Thank you for the additional links!