No there isn't any value you can set the expiration so it is infinite. You'll just need to set it to something really long.
As you know, if you do not set an expiration the cookie then only lives for the length of the session (when the browser is closed), which is definitely not what you want.
You can also use slidingexpiration=true
so that whenever a user comes back to the site, the expiration date on the cookie is refreshed to be Today + Timeout
instead of DateInitiallyIssued + Timeout