Yes, we have had the same issue with our portal. You can't enable SSL
for just one or two menu items, you need to put all your site in HTTPS
to use the secondary page in Secure mode.
The other way is to create a sub-site and link from the main site to
the "secure site".
What we did is to handle the URL rewrite in Apache in front of
application servers, to force https in the selected menu items (urls).
take a look to
www.battleforge.com
Regards,
Bruno.