SSL and CDN = multiple hosts, single session still possible?

So my company is looking at implementing a Content delivery network. A by product of this is that it seems they want us to break out our secure traffic onto a different host name so that we can cname our www in addition to any other hostnames we want to alias. Also depending on wich CDN we choose we may get SSL accleration w/ a certificate for the CDN.

So if eventually all the traffic for the websites makes it back to my domain, is there anyway to keep the seesion data for an order as they move between www.foo.com and ssl.foo.com? I currently am using cookies to track sessions and keeping them inprocess (fastest solution), but I do have a SQL server behind the website as well (windows 2003, sql2005).

I think I have two options, but I don't know exactly how the second works.
1) I could just serialize the user's order and either pass it as a query string, or store it in a cookie that was scoped to foo.com (so www.foo.com and ssl.foo.com can both read it).
2) Do something so that as the user gets passed from www.foo.com to ssl.foo.com the sessionID for the user comes along for the ride, since both host names will be running on the same server in the same application.

Anyway I'm sure this problem has been solved before so I'm curious as to what people have down to make this work.

Thanks,
Joel Barsotti