No on-line way - yet; there was an official announcement of a website overhaul, complete with individual usernames and passwords/PINs. This would pave the way for on-line account management / ressies, but nothing official has been said about that.
You can do a ressie via email; I've never done it, but some folks here have. I believe that there's a link on the website. I just like to talk to a human....