noob question about ssl

I'm using nginx as a reverse-proxy front-end for an ajax web app. This web app has lots of sections accessible to the general public, plus it has "member" areas where they have to be logged in. I use SSL for the members, letting nginx handle the encryption and always connecting to the web app unencrypted. But, switching from a non-ssl connection to one that is encrypted means the web app has to reload, which takes time (well, in order for me to switch to ssl mode, I have to direct the visitor to the https version of the URL, which in effect loads a new session).

Is there a way to instruct nginx switch to an encrypted connection without forcing a URL reload? I don't want to redirect all connections to always use ssl, as this is a large app/site and it would put too much load on the server.

Thanks,
Jay